[js] 第1天 用递归算法实现，数组长度为5且元素的随机数在2-32间不重复的值 about fe-interview HOT 449 OPEN

    var arr = new Array(5);
    var num = randomNumber();
    var i = 0;
    randomArr(arr,num);
    function randomArr(arr,num) {
        if (arr.indexOf(num)< 0){
            arr[i] = num;
            i++;
        } else {
            num = randomNumber();
        }
        if (i>=arr.length){
            console.log(arr);
            return;
        }else{
            randomArr(arr,num)
        }
    }
    function randomNumber() {
        return Math.floor(Math.random()*31 + 2)
    }

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// 6 行写完
function buildArray(arr, length, min, max) {
    var num = Math.floor(Math.random() * (max - min + 1)) + min;
    if (!arr.includes(num)) { arr.push(num); }
    return arr.length === length ? arr : buildArray(arr, length, min, max);
}
var result = buildArray([], 5, 2, 32);
console.table(result);

补充：
题目要求”生成一个（2－32）之间的随机整数rand“，既然是随机，我觉得意为取值到区间内各数的概率应该是相等的。所以像这样的写法是不严谨的：

// 在 2 - 5 区间内生成随机数
var min = 2, max = 5;
var result = Math.max(min, Math.ceil(Math.random() * max));
// 参数一 param1 恒等于 2
// 参数二 param2 在 [0, 5] 之间等概取值
// 可能性见下
// param1 2 2 2 2 2 2
// param2 0 1 2 3 4 5
// result 2 2 2 3 4 5

可见 result 取到 2 的概率大于 3/4/5。 @linghucq1

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考虑一下扩展性

function insertArr(arr, i = 0, min = 2, max = 32) {
  const num = Math.max(min, Math.ceil(Math.random() * max))
  if (!arr[arr.length - 1]) {
    if (!arr.includes(num)) { 
      arr[i++] = num
    }
    return insertArr(arr, i) 
  }
  return arr 
}
const arr = new Array(5);
const result = insertArr(arr)

这里的随机数算法是有问题的，具体参见下面 @likeke1997 的答案。另外用四舍五入也是不对的，因为最小值和最大值只有其它值概率的一半。

仔细一看，虽然自定义了最大最小参数，但是递归的时候没有传入，所以并没有卵用。i 参数的初衷是自定义从哪里开始插入，实用性也没有 @likeke1997 的 length 参数来的好。

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var arr = []; //数组
var num = 2 + Math.floor(Math.random() * 30); //生成 2-32 内的随机数
var n = 0; //记录数回调次数
var setArr = function(num){ //生成数组长度为5且元素的随机数在2-32间不重复的值
if(arr.length === 5){ //数组长度为5便跳出循环
return console.log(arr);
}
if(arr.every((v) => (v !== num))){ //判断数组中是否没有该值
arr.push(num);
}
n++;
setArr (Math.floor(Math.random()*(31)+2));
}
setArr (num);

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var arr = new Array(5);
function insertRandom(n) {
  if (n < 0) return
  let tmp = Math.floor(Math.random() * 31 + 2)
  if (arr.indexOf(tmp) !== -1) return insertRandom(n)
  arr[n] = tmp
  return insertRandom(n - 1)
}
insertRandom(arr.length - 1)

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var arr=new Array(5);
var randomNum=2+Math.floor(Math.random()*30);
var i=0;
function ArrPushItem(arr,randomNum)
{
if(arr.indexOf(randomNum)>-1)
{
randomNum=2+Math.floor(Math.random()*30);
}
else{arr[i]=randomNum;
i++;
randomNum=2+Math.floor(Math.random()*30);}
if(i==arr.length)
{return arr;}
else
{ArrPushItem(arr,randomNum)}
}
ArrPushItem(arr,randomNum)

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var arr = new Array(5);
var num = Math.floor(Math.random()* (31) + 2);
function numsInterative(num) {
  if (arr.length == 5) {
    console.log(arr);
  }
  if (!arr.includes(num)) {
    arr.push(num)
  }
  numsInterative(Math.floor(Math.random()* (31) + 2))
}
numsInterative(num)

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function buildArray(arr, length, min, max) {
    if (!Array.isArray(arr)) arr = []
    if (length < 1) return []
    if (arr.length === length) return arr
    const random = Math.random() * (+max - +min) + +min
    if (!arr.includes(random)) arr.push(random)
    return buildArray(arr, length, min, max)
}

buildArray([], 5, 2, 32)

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function foo(arr) {
	arr = arr || []

	if (arr.length >= 5) {
		return arr
	}

	var n = 2 + Math.floor(Math.random() * 31)

	if (arr.indexOf(n) == -1) {
		arr.push(n)
	}

	return foo(arr)
}

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function returnRandomArr(max, min, length, arr = []) {
  arr.push(Math.floor(Math.random() * (max - min)) + min);
  arr = Array.from(new Set(arr))
  return arr.length < length ? returnRandomArr(max, min, length, arr) : arr
}
let arr = returnRandomArr(32, 2, 5)
console.log(arr)

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var arr = new Array(5);
var i= 0;
function randomHandle () {
var num = 2 + Math.floor(Math.random() * 30);
if (arr.indexOf(num) < 0) {
arr[i] = num;
i ++;
}
(i < 5) && randomHandle();
}
randomHandle();

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function setArr(arr) {
      if(arr.length==5) return;
      const num = parseInt((Math.random())*31+2);
      if(arr.indexOf(num) === -1) arr.push(num)
      return setArr(arr);
}

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const arr = []
const getRandom = () => {
	const num = parseInt(Math.random() * 100, 10) + 2
	if (arr.length >= 5) return arr
	if (num <= 32 && arr.indexOf(num) === -1){
		arr.push(num)
	}
	getRandom()
}
getRandom()
console.log(arr)

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// 尾递归
function randomArr(count, arr = []) {
  if(count === 0) return arr;
  let num = Math.floor(Math.random() * 31) + 2;
  if(!arr.includes(num)) {
    arr.push(num);
    count--;
  }
  return randomArr(count, arr);
}

console.log(randomArr(5))

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为啥要 return insertArr(arr, i) ,把return去掉也可以

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7行搞定 Set去重是真好用

  let arr = [];

  (function insertNumber() {
    if (arr.length === 5) return;
    arr.push(Math.floor(Math.random() * 31 + 2));
    arr = [...new Set(arr)];
    insertNumber();
  })()
  console.log(arr);

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     /***
     * 性能达到最优》考虑时间复杂度（避免使用Math.random去随机到不重复数字）
     * 最终优化,当如果取随机数为30个的时候，那么最后面几个数会很小几率随机到，优化思路，将随机 
     * 数初始时放置数组，取值后剔除
     */
    function getRandom1(n, min = 2, max = 32) {
      //如果取值数量大于最大随机数，将最随机数最大值提高
      if (n > (max - min)) {
        max += n - (max - min);
      }
      //使用创建的指定数量空数组 keys 下标直接填充，避免 for循环填充
      var initArray = Array.from(new Array(max + 1).keys()).splice(min);

      return function insert(resArrayRandom) {
        if (resArrayRandom.length == n) {
          return resArrayRandom;
        }
        //获取剩余数组随机下标
        var indexRandom = parseInt(Math.random() * initArray.length);
        resArrayRandom.push(initArray[indexRandom]);
        initArray.splice(indexRandom, 1);
        return insert(resArrayRandom);
      }([])
    }

    let beginTime2 = new Date().getTime();
    getRandom1(1000)
    console.log("优化取随机数 后耗时：", new Date().getTime() - beginTime2)

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function getUNumber(arr, min, max) {
var rand = Math.floor(Math.random() * (max - 1)) + min;
if (arr.indexOf(rand) === -1) {
return rand;
} else {
return getUNumber(arr, min, max);
}
}

function getRandomArrayByLength(len) {
    if (len === 1) {
        return [getUNumber([], 2, 32)];
    } else {
        var arr = getRandomArrayByLength(len - 1);
        var rand = getUNumber(arr, 2, 32);
        arr.push(rand);
        return arr;
    }
}

var newArray = new Array(5);
console.log(getRandomArrayByLength(newArray.length));

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function createArray(len, minNum, maxNum) {
  var createRandom = (min, max) => { return (Math.round((max - min) * Math.random()) + min)};
  var arr = new Array(len), count = 0;
  function run() {
    var num = createRandom(minNum, maxNum);
    (!arr.includes(num)) && (arr[count] = num, count++);
    (count < len) && (run());
  }
  run(); return arr;
}
console.log(createArray(5, 2, 32));

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只需要 6 行代码：

function getFiveRandomSet(arr) {
    	if(arr.length >= 5) return arr
    	const randomNumber  = ~~ (Math.random() * 30 + 2)
    	const newArr = Array.from(new Set(arr.concat(randomNumber)))
    	return getFiveRamdomSet(newArr)
    }
getFiveRandomSet([])

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function randomArray(length: number, min: number, max: number, cache?: {[key:number]: boolean}): number[] {
  cache = cache || {}
  const randomNum = Math.floor(Math.random() * (max - min + 1) + min)
  if (!cache[randomNum]) {
    length -= 1
    cache[randomNum] = true
  }
  return length ? randomArray(length, min, max, cache) : Object.keys(cache).map(Number)
}

randomArray(5, 2, 32)

补充一下 Object 跟 Array.prototype.includes 去重性能对比代码：

  const arr = []
  const obj = {}
  const len = 100000

  for (let i = 0; i <= len; i++) {
    arr.push(i)
    obj[i] = true
  }

  console.time('Array.includes')
  for (let i = 0; i <= len; i++) {
    arr.includes(i)
  }
  console.timeEnd('Array.includes')

  console.time('Obnject.keys')
  for (let i = 0; i <= len; i++) {
    obj[i]
    if (i === len) {
      Object.keys(obj).map(Number)
    }
  }
  console.timeEnd('Obnject.keys')

结果图：

Array.prototype.includes 规范，我们可以看出 includes 是通过遍历去查询是否存在 searchElement 元素的，这也是其速度不及 对象索引 快的原因了

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    var arr = new Array(5),
          len = arr.length;
    function arPush() {
        if( len != 0 ) {
            len --;
            let n = Math.floor((Math.random() * 31) + 2);
            each(n, len) ? (arr[len] = n) : len ++;
            arPush();
        }
    }
    function each(index, i) {
        if( i > arr.length - 1) return true; 
        return arr[i] == index ? false : (each(index,i + 1));
    }
    arPush()

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function createArr(arr) {
let res = arr || [];
let num = parseInt(Math.random() * (32 - 2) + 2);
if (!res.includes(num)) res.push(num);
if (res.length < 5) createArr(res)
return res
}
let b = createArr()

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`
function main(len = 5){

let list = [];

for(let i = 2; i <= 32; i++){   // 这里生成取值范围列表

	list.push(i);

}

function getRandom(start, end){

	let rang = end - start;

	return Math.floor(Math.random() * rang) + start;

}

function recursion(arr = []){

	let index = getRandom(0, list.length);

	let val = list.splice(index, 1).join();  //随机到后移除出列表(可避免随机到重复值)

	arr.push(val);

	return arr.length >= len ? arr : recursion(arr);  //根据结束条件去递归

}

return recursion();

}
`

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• 照顾通用性的解法

function randNumbers(n, lb, rb, arr = []) {
    if (arr.length === n) return arr
    const rand = Math.round(Math.random() * (rb - lb)) + lb
    if (arr.includes(rand)) return randNumbers(n, lb, rb, arr)
    else return randNumbers(n, lb, rb, arr.concat(rand))
}

console.log(randNumbers(5, 2, 32))

• 稍短一些的解法

function randNumbers(arr = []) {
    if (arr.length === 5) return arr
    const rand = Math.round(Math.random() * 30) + 2
    if (arr.includes(rand)) return randNumbers(arr)
    else return randNumbers(arr.concat(rand))
}

console.log(randNumbers())

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只需要 6 行代码：

function getFiveRamdomSet(arr) {
    	if(arr.length >= 5) return arr
    	const randomNumber  = ~~ (Math.random() * 30 + 2)
    	const newArr = Array.from(new Set(arr.concat(randomNumber)))
    	return getFiveRamdomSet(newArr)
    }
getFiveRamdomSet([])

step1 就跪了, 6行代码, 呵呵了.

不会发言没人把你当弱智

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const randomArr = (arr = new Array(5), i = 0) => {
  if (i >= arr.length) {
    return arr
  }
  let num = Math.floor((Math.random() * 31)) + 2
  if (arr.indexOf(num) === -1) {
    arr[i++] = num
  }
  return randomArr(arr, i)
}
console.log(randomArr())

10 行代码，封装成函数，调用 randomArr 即可生成一个符合要求的数组，使用递归的方式。

还可以为函数提供随机数生成范围，数组长度等参数，进一步封装。

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感觉ES6比较简洁，投机取巧一下。好久没写ts整两句。~~~很菜

// let sets: any = new Set([...Array(5)]);
// sets.delete(undefined);
// 前两行 等同于第四行。不明白 a目的何在
let sets: any = new Set();
!function getNum(sets): any {
    let rand = Math.floor(Math.random() * 31 + 2);
    return !sets.has(rand) || sets.size < 5 ? (sets.size < 5 ? getNum(sets.add(rand)) : sets) : sets;
}(sets);
console.log(sets);
// 如有错误 可以指正哈

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let arr = [];
// 指定范围随机整数
let getRandomNum = (min, max) => { return min + Math.round((max - min) * Math.random())};
(function addArr (num) {
  if (arr.length === 5) return
  // 重复数据检测
  if (!arr.includes(num)) arr[arr.length] = num
  // 递归执行
  addArr(getRandomNum(2, 32))
})(getRandomNum(2, 32))
console.log(arr = arr.sort((a, b) => a-b))

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function generateArray(arr, length, max, min) {
    if (arr.length === length) {
        return arr
    }
    const rand = Math.ceil(Math.random()*(max - min)) + min
    if (arr.indexOf(rand) === -1) {
        arr.push(rand)
    }
    return generateArray(arr, length, max, min)
}

generatorArray([], 5, 32, 2)

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function numerrandom() {
return Math.floor(Math.random()*31 + 2)
}
function test(arr, num) {
if (arr.length === 5) {
return arr
} else if (arr.indexOf(num) >-1) {
return test(arr, numerrandom())
}
else {
arr.push(num)
return test(arr, numerrandom())
}
}

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function getArr(arr = []) {
    if (arr.length === 5) {
        return arr;
    }
    const ran = Math.floor(Math.random() * 31) + 2;
    if (!arr.includes(ran)) {
        arr.push(ran);
    }
    return getArr(arr);
}
console.log(getArr());

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点评：
知识点：递归、随机数
难点：1颗星
这道题主要是想考递归的用法，同时顺带考了生成指定范围的随机数方法。
@yxkhaha @qingleizhang123

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  function getRandomArr(arr, len,) {
    if (arr.length === len) { return arr }
    let rndNum = Math.floor(Math.random() * (32 - 2 + 1) + 2)
    if (arr.indexOf(rndNum) > -1) return getRandomArr(arr, len)
    else {
      arr.push(rndNum)
      return getRandomArr(arr, len)
    }
  }
  console.log(getRandomArr([], 5))

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function randomNum(){
    return Math.floor(Math.random() * 32 + 2)
}
function arrFunc(arr, num){
    if(arr.length >= 5) return arr;
    if(!arr.includes(num)){
	arr.push(num);
    }
    return arrFunc(arr, randomNum())
}
arrFunc(arr, randomNum())

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var arr = []
var num 
console.log(num)
function newArr(arr, num) {
  if (arr.length >= 5) {
    return
  } else {
    num = Math.floor(Math.random() * 30) + 2
    return arr.push(num) + newArr(arr, num)
  }
}
newArr(arr, num)
console.log(arr)

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const arr = []
const getRandom = () => {
	const num = parseInt(Math.random() * 100, 10) + 2
	if (arr.length >= 5) return arr
	if (num <= 32 && arr.indexOf(num) === -1){
		arr.push(num)
		getRandom()
	} else {
		getRandom()
	}
}
getRandom()
console.log(arr)

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    let randomArr = [];
    function recursiveNumber(randomArr, currentLoop,min, max) {
        if (currentLoop <= 0) return;
        const curRandomNumber = min + parseInt(Math.round(Math.random() * (max -min)));
        if (randomArr.filter(res => res === curRandomNumber).length) {
            recursiveNumber(randomArr, currentLoop, min, max);
        } else {
            randomArr.push(curRandomNumber);
            recursiveNumber(randomArr, currentLoop - 1, min, max);
        }
    };
    recursiveNumber(randomArr, 5, 2, 32);

这是我的答案，大家可以参考下

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function outPut() {
	var num = Math.random()*10+2;
	if(set.size <= 5) {
		set.add(Math.round(num));
		outPut();
	} else {
	        console.log([...set]);
	}
}
var set = new Set();
outPut();

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function gen(arr, n) {
if (n <= 0) {
return;
}
let randomItem = 2 + 30 * Math.random();
if (arr.indexOf(randomItem) !== -1) {
return gen(arr, n);
} else {
arr.push(randomItem);
return gen(arr, n-1);
}
}

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function buildArray2 () {
        // Set实现
        function createRandom () {
            return Math.floor(Math.random() * 30 + 2)
        }
        let arr = new Set()
        function arrayRandom () {
            if (arr.size < 5) {
                arr.add(createRandom())
                arrayRandom()
            } else {
                arr = [...arr]
                console.log('---' + arr)
            }
        }
        arrayRandom()
    }

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答案超过15行代码的 好意思留答案吗？

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// 9行
var set = new Set();
addRandom();

function addRandom(){
  if(set.size<5){
    let random = Math.floor(Math.random()*30+2);
    set.add(random)
    addRandom();
  }
}

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const arr = [];
let idx = 0;
function filter() {
  const num = Math.floor(Math.random() * 31 + 2);
  while (idx < 5) {
    if (!arr.includes(num)) {
      arr.push(num);
      idx++;
    }
    filter();
  }
}

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const getRandomNumber = (min = 2, max = 32) =>
  parseInt(Math.random() * (max - min + 1) + min, 10);

const arr = new Array(5);

const getUniqNumber = (arr, index, num, limit = 5) => {
  if (index >= limit) {
    return arr;
  }

  if (arr.includes(num)) {
    getUniqNumber(arr, index, getRandomNumber(), limit);
  } else {
    arr[index] = num;
    getUniqNumber(arr, index + 1, getRandomNumber(), limit);
  }
};

getUniqNumber(arr, 0, getRandomNumber());

console.log(arr);

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function fn (arr, size) {
  if (arr.length === size) return arr	
  var num = Math.floor(Math.random() * 30) + 2
  if (!arr.includes(num)) arr.push(num)
  return fn(arr, size)
}

fn([], 6)

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const arr = new Array(5).fill(null);
const rand = () => Math.floor(Math.random() * 30 + 2);

function insertToArr(arr) {
if (arr.filter(Boolean).length >= 5) return arr;
const randVal = rand();
~arr.indexOf(randVal) ? null :arr[arr.filter(Boolean).length] = randVal;
return insertToArr(arr);
}
console.log(insertToArr(arr))

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const arr = new Array(5);
const funcRandomValue = () => {
    return Math.floor((Math.random() * 31) + 2);
};
let a = 0;
const func1 = (cont) => {
    if (arr.indexOf(cont) === -1) {
        arr[a] = cont;
        a = a + 1;
        if (a !== 5) func1(funcRandomValue());
    } else {
        func1(funcRandomValue());
    }
}
func1(funcRandomValue());

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function randArr(arr,randNum){
    var rand = Math.floor(Math.random()*30 + 2);
    if(arr.length < 5){
        if(arr.some(i=>{i === randNum})){
            randArr(arr,rand)
        }else{
            arr.push(randNum)
            randArr(arr,rand)
        }
    }else{
        console.log(arr)
    }
}
randArr([],Math.floor(Math.random()*32 + 2))

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let getRandomArr = function(e){
let arr = e ? e : []
let randomNum = getRandomNum()
if(!arr.includes(randomNum)){
arr.push(randomNum)
}
return arr.length === 5 ? arr : getRandomArr(arr)
}
let getRandomNum = function(){
return Math.floor(Math.random()*31+2)
}

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看问题，我还以为要自己实现随机数算法，结果进来大家都用 Math.random

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function randomNumArr(min, max, len, arr: number[] = []) {
  if (arr.length === len) {
    return arr;
  }

  let num = randomNum(min, max);
  while (arr.includes(num)) {
    num = randomNum(min, max);
  }
  arr.push(num);
  return randomNumArr(min, max, len, arr);
}

function randomNum(min, max) {
  return min + Math.round(Math.random() * (max - min));
}

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var arr =[]; 
var rand; 
var i = 0; 
function getArr(arr){ 
rand = Math.floor(Math.random()*31+2);
if(arr.length==5) {
console.log(arr); 
i=0; 
arr =[]; 
return;} 
if(arr.length==0 || arr.every((item)=>(item!=rand))) 
{ arr[i] = rand; i++; } 
getArr(arr) } 
getArr(arr)

from fe-interview.

function randArr(arr=[]){
let rand = Math.ceil(Math.random()*30+2);
if(arr.indexOf(rand)===-1&&arr.length<5){
arr.push(rand)
return randArr(arr)
}else{
return arr;
}
}

from fe-interview.

function result () {
    let arr = new Array(5).fill(undefined)
    const fill = () => {
	let number = 2 + Math.floor(Math.random()*30)
	let index = arr.findIndex(item => item === undefined || item === number);
	if ( index !== -1) {
		arr.splice(index, 1, number);
		fill()
	}
    }
    fill()
    return arr
}
console.log(result())

from fe-interview.

function padArray(arr, i, min, max) {
  const length = arr.length
  if (arr[length - 1]) return arr
  const random = Math.min(Math.ceil(Math.random() * max + min), max - 1)
  if (!arr.includes(random)) arr[i++] = random
  return padArray(arr, i, min, max)
}
console.log(padArray(new Array(5), 0, 2, 32))

from fe-interview.

function randomArr(count, min, max, arr = []) {
    if (arr.length === count) return arr
    let randomNumber = ~~(Math.random() * (max - min + 1) + min)
    return randomArr(count, min, max, [...new Set([...arr, randomNumber])])
}
randomArr(5, 2, 32)

缺点：函数的执行与函数名 randomArr 耦合在了一起
优化：给内部函数命名

function randomArr(count, min, max, arr = []) {
    return (function fn(count, min, max, arr = []) {
        if (arr.length === count) return arr
        let randomNumber = ~~(Math.random() * (max - min + 1) + min)
        return fn(count, min, max, [...new Set([...arr, randomNumber])])
    })(count, min, max, arr = [])
}

from fe-interview.

const arr = new Array(5);

const randNum = () => 2 + Math.floor( Math.random() * 30 );

let i = 0;

const randFun = () => {

if( i == arr.length ) return

!arr.includes( randNum() ) && (arr[i] = randNum() ) && i++;

randFun()

}

randFun();

from fe-interview.

var arr = []; //数组
var num = 2 + Math.floor(Math.random() * 30); //生成 2-32 内的随机数
var n = 0; //记录数回调次数
var setArr = function(num){ //生成数组长度为5且元素的随机数在2-32间不重复的值
if(arr.length === 5){ //数组长度为5便跳出循环
return console.log(arr);
}
if(arr.every((v) => (v !== num))){ //判断数组中是否没有该值
arr.push(num);
}
n++;
setArr (Math.floor(Math.random()*(31)+2));
}
setArr (num);

step1就跪了. 生成一个长度为5的空数组arr。

const arr = [];
arr.length = 5;
const createNum = () => parseInt(Math.random() * 31) + 2;
pushNum = () => {
if(arr[4]) return;
let num = createNum();
if(!arr.includes(num)) {
arr.splice(arr.findIndex(item => !item), 1, num);
}
pushNum();
}
pushNum();

from fe-interview.

只需要 6 行代码：

function getFiveRamdomSet(arr) {
    	if(arr.length >= 5) return arr
    	const randomNumber  = ~~ (Math.random() * 30 + 2)
    	const newArr = Array.from(new Set(arr.concat(randomNumber)))
    	return getFiveRamdomSet(newArr)
    }
getFiveRamdomSet([])

step1 就跪了, 6行代码, 呵呵了.

from fe-interview.

var arr = []; //数组
var num = 2 + Math.floor(Math.random() * 30); //生成 2-32 内的随机数
var n = 0; //记录数回调次数
var setArr = function(num){ //生成数组长度为5且元素的随机数在2-32间不重复的值
if(arr.length === 5){ //数组长度为5便跳出循环
return console.log(arr);
}
if(arr.every((v) => (v !== num))){ //判断数组中是否没有该值
arr.push(num);
}
n++;
setArr (Math.floor(Math.random()*(31)+2));
}
setArr (num);

step1就跪了. 生成一个长度为5的空数组arr。

const arr = [];
arr.length = 5;
const createNum = () => parseInt(Math.random() * 31) + 2;
pushNum = () => {
if(arr[4]) return;
let num = createNum();
if(!arr.includes(num)) {
arr.splice(arr.findIndex(item => !item), 1, num);
}
pushNum();
}
pushNum();

第一：学会格式化代码
第二：学会合理使用表情
第三：学会使用 markdown
都 9012 年了还不会学 es6 ?

from fe-interview.

var arr = []; //数组
var num = 2 + Math.floor(Math.random() * 30); //生成 2-32 内的随机数
var n = 0; //记录数回调次数
var setArr = function(num){ //生成数组长度为5且元素的随机数在2-32间不重复的值
if(arr.length === 5){ //数组长度为5便跳出循环
return console.log(arr);
}
if(arr.every((v) => (v !== num))){ //判断数组中是否没有该值
arr.push(num);
}
n++;
setArr (Math.floor(Math.random()*(31)+2));
}
setArr (num);

step1就跪了. 生成一个长度为5的空数组arr。
const arr = [];
arr.length = 5;
const createNum = () => parseInt(Math.random() * 31) + 2;
pushNum = () => {
if(arr[4]) return;
let num = createNum();
if(!arr.includes(num)) {
arr.splice(arr.findIndex(item => !item), 1, num);
}
pushNum();
}
pushNum();

第一：学会格式化代码
第二：学会合理使用表情
第三：学会使用 markdown
都 9012 年了还不会学 es6 ?
戾气太重, 格式化代码确实是我没注意, 直接在评论里写了,而且我接下来的回复也没打算用什么格式化, 另外md经常使用,还需要提醒我学吗? 表情有问题? 表情不就是用来自嘲或者嘲讽别人的吗? 没看出来我代码里哪里必须要使用es6的地方啊? 你可以指出来.
我说的step1 跪了, 难道错了吗? 你自己看, 要求是: a) 生成一个长度为5的空数组arr。你生成了吗? 偷奸耍滑, 直接用空数组push了, 虽然能得到正确结果, 但是没有按要求来. a步骤并不是多余的, 其中影藏一个考点是不使用for,等循环语句, 来判断是否达到5个正确的值了, 以及当前产生的数字要放到数组的那个位置, 也还有就是生成 空数组的技巧. const arr = Array(5); 或者 const arr = new Array(5); 或者 const arr = []; arr.length = 5; 这几种方式都能生成空的, 长度为5的数组. 你的代码直接跳过了这个要求, 我指出来的不对吗?我的代码有问题, 你可以指出来(要具体), 可以嘲讽, 但是请不要人身攻击.

from fe-interview.

let arr=[ ];
function fn(arr){
    if(arr.length>=5) return arr;
    let ramdom=Math.floor(Math.random()*31+2);
    if(arr.includes(ramdom)){ return fn(arr);}
    else {return fn([...arr,ramdom]);}
}

console.log(fn(arr))

from fe-interview.

看问题，我还以为要自己实现随机数算法，结果进来大家都用 Math.random

启动编辑器的一瞬间，我的脑海中随机出现了 1 3 5 7 9五个数字，和算法生成随机数一样，所以不用再生成了。

from fe-interview.

var arr = [];
		toarr();

		function toarr() {
			var num = randomNum();
			if (arr.length < 5) {
				if (arr.indexOf(num) < 0) {
					arr.push(num);
					toarr();
				} else {
					toarr();
				}
			} else {
				console.log(arr);
			}
		}
		function randomNum() {
			return Math.floor(Math.random() * (32 - 2)) + 2;
		}

from fe-interview.

var array = new Array(5);
function insert(array, index) {
    if (array.length === index) {
        return array;
    }
    var number = parseInt(Math.random() * (32 - 2 + 1) + 2, 10);
    if (array.includes(number)) {
        return insert(array, index);
    } else {
        array[index] = number;
        return insert(array, ++index);
    }
}
console.log(insert(array, 0));

from fe-interview.

九行代码

var arr = new Array(5),index=0;
function create () {
    var rand = Math.floor(Math.random()*31 + 2);
    if (arr.indexOf(rand) === -1 && index <5){
        arr[index] = rand;
        ++index;
	create();
    } else if(index===6) return;
}

from fe-interview.

8 行

function randarr(arr) {
	let rand = parseInt((Math.random()*30+2).toFixed(0))
	if (arr.length === 5) { console.log(arr);return }
	arr.indexOf(rand) === -1 ? arr.push(rand) && randarr(arr) : randarr(arr)
}
let arr = []
randarr(arr)	

from fe-interview.

const random = (min, max)=> () => Math.random() * (max - min) + min
let random2to32 = random(2,32)
function createRandomNum(length) {
    let arr = new Set()
    function creatNum(arr, total) {
        if(arr.size===total)   return arr 
          let newRandoms = Math.floor(random2to32())
          if(!arr.has(newRandoms)){
            arr.add(newRandoms)
          }
        return  creatNum(arr, total)
    }
    let returnArr = creatNum(arr, length)
    return [...returnArr]
}
console.log(createRandomNum(5));

from fe-interview.

只需要 6 行代码：

function getFiveRamdomSet(arr) {
    	if(arr.length >= 5) return arr
    	const randomNumber  = ~~ (Math.random() * 30 + 2)
    	const newArr = Array.from(new Set(arr.concat(randomNumber)))
    	return getFiveRamdomSet(newArr)
    }
getFiveRamdomSet([])

step1 就跪了, 6行代码, 呵呵了.

不会发言没人把你当弱智

淡定。朋友

from fe-interview.

let arr = [];
let i = 0;

// 生成2~32随机数
function span () {
let num = Math.floor(Math.random() * 31) + 2;
return num;
}

function arrRes () {
let newNum = span();
// 数组的长度为5
if(i < 5) {
if (!arr.includes(newNum)) {
arr.push(newNum) // 每增加一项让i+1
i++;
arrRes() // 递归
}else {
arrRes() // 如果有随机数相同的情况也要进行递归，但是i值不变
}
}
}
arrRes()
console.log(arr)

from fe-interview.

function randomArr(arr){
  arr.add(Math.floor(Math.random()*31+2))
  if(arr.size < 5) randomArr(arr)
  return [...arr]
}
console.log(randomArr(new Set()))

from fe-interview.

(function getRandomArrayByRange(arr = new Set(), len = 5, min = 2, max = 32) {
  arr.add(Math.floor(Math.random() * (max - min + 1) + min))
  return arr.size < len ? getRandomArrayByRange(arr, len, min, max) : [...arr]
})()

from fe-interview.

function getRandomNum(arr) {
let val = Math.floor(Math.random()*31 + 2);
if (arr.includes(val)) {
return getRandomNum(arr);
} else {
return val;
}
}
function createArr(arr) {
if (arr.length === 5) {
console.log(arr);
return;
}
let val = getRandomNum(arr);
arr.push(val);
createArr(arr);
}
createArr([]);

from fe-interview.

let set = new Set();
function test() {
if (set.size() === 4) set.add(Math.random() * 30 + 2)
}
let arr = Array.from(set)

from fe-interview.

let a = new Array(5)
function addArr(arrNo, num) {
if (num == 5) {
return
} else {
var arrNum = Math.floor(Math.random() * 31 + 2)
var n = arrNo.find(e => e == arrNum)
if (n == undefined) {
arrNo.splice(num,1,arrNum)
num ++
}
addArr(arrNo, num)
}
}
addArr(a, 0)

from fe-interview.

那些比几行代码的,我不敲回车可以再少几行!!!!!!!!!

from fe-interview.

获取（min ~ max）范围内的随机整数

Math.floor(Math.random() * (max - min + 1) + min)

输出长度为5且内容不重复的arr

let arr = new Array(5)
let printArr = (arr, i = 0) => {
  let rand = Math.floor(Math.random() * 31 + 2)
  if (i < arr.length) {
    if (!arr.includes(rand)) {
      arr[i++] = rand
    }
    printArr(arr, i)
  }
  return arr
}
printArr(arr) // 调用

from fe-interview.

https://codepen.io/9lk/pen/OKPwOo

// 1.生成一个长度为5的空数组arr。
var genArray = length => (Array.from({length}))

// 2.生成一个（2－32）之间的随机整数rand。
var genRandNum = () => Math.ceil(Math.random()*30+1)

// 3.数组长度为5且元素的随机数在2-32间不重复的值
var reduceNums = (length, set=[]) => {
  if(set.size>= length) return Array.from(set)
  
  return reduceNums(length, new Set([genRandNum(), ...set]))
}

from fe-interview.

function createArray(arr = []) {
  // Get a random between 2 and 32
  const randomNum = 2 + Math.floor(Math.random()*31)
  // Cannot be repeated with the number in arr
  !arr.includes(randomNum) && arr.push(randomNum)
  // Create a array of length 5
  arr.length < 5 && createArray(arr)
  return arr
}

from fe-interview.

递归用了2行代码实现。
固定N=5次循环，100%命中。
除了第一次需要生成样本数据略慢外，后续调用都非常快速。
不会影响其他同步函数执行，不影响渲染。
欢迎讨论性能更好的算法。

"use strict";

function Range ( m, n, step ) {
  this._sample = this._generateSample( m, n, step );
}

Range.prototype = {
  setSample ( sample = [] ) {
    this._sample = Promise.resolve( sample );
  },

  async shuffle ( size ) {
    if ( size ) {
      const sample = Array.from( await this._sample );
      const n = sample.length;

      if ( n < size ) {
        throw new Error(
          `Shuffle size must not exceed the range size. ` +
          `Expected the maximum value of size is ${ n }, but the actual value is ${ size }.`
        );
      }

      const result = new Array( size );
      console.time( `shuffle perf` );
      this._shuffle( size, sample, n, result );
      console.timeEnd( `shuffle perf` );

      return result;
    }

    return [];
  },

  async _generateSample ( m = 0, n = 0, step = 1 ) {
    m > n && ( [ m, n ] = [ n, m ] );
    step = Math.abs( step );
    const sample = [];
    do {
      sample.push( n );
    }
    while( m <= ( n -= step ) );
    return sample;
  },

  _shuffle : ( () => {
    const random = Math.random;
    function shuffle ( size, sample, n, result ) {
      result[ size -= 1 ] = sample.splice( random() * n >> 0, 1 )[ 0 ];
      size && shuffle( size, sample, n - 1, result );
    }
    return shuffle;
  } )(),
};

const range = new Range( 2, 32 );
console.log( await range.shuffle( 5 ) );

from fe-interview.

let arr = [];
random(arr);
function random(arr) {
    if (arr.length < 5) {
        let rand = Math.floor((Math.random()*30)+2);
        if (arr.indexOf(rand) === -1) {
            arr.push(rand);
        }
        random(arr);
    }
}

from fe-interview.

var randomArr = function(arr=[],length=5,min=2,max=32){
var randomNumber = Math.floor(Math.random()*(max-min))+min;
if(arr.length<length){
if(!arr.includes(randomNumber)){
arr.length === 0 ? arr[0] = randomNumber : arr[arr.length] =
randomNumber;
}
randomArr(arr);
}

		if(arr.length==length){
			return arr;
		}
	}
	console.log('result_arr',randomArr())

from fe-interview.

function randomArr(arr = new Array(5), len = 5) {
    if (len === 0) {
        return arr
    }

    const num = ~~(Math.random() * 31) + 2

    if (arr.includes(num)) {
        return randomArr(arr, len)
    }

    arr[--len] = num
    return randomArr(arr, len)
}

from fe-interview.

let arr = new Array(5);
for (let i = 0; i < arr.length; i++) {
let num = genNum();
arr[i] = num;
}

function genNum() {
let num = Math.floor(Math.random() * 31 + 2);
if (arr.indexOf(num) < 0) {
return num;
} else {
return genNum();
}
}

console.log(arr)

from fe-interview.

let arr = new Array(5), index = 0;
function deepLoop(arr) {
if(index > 4) {
return
}
let arnd = Math.floor(Math.random()*31 + 2);
if(!arr.includes(arnd)) {
arr[index++] = arnd;
}
deepLoop(arr);
}

from fe-interview.

    var arr = new Array(5);
    var num = randomNumber();
    var i = 0;
    randomArr(arr,num);
    function randomArr(arr,num) {
        if (arr.indexOf(num)< 0){
            arr[i] = num;
            i++;
        } else {
            num = randomNumber();
        }
        if (i>=arr.length){
            console.log(arr);
            return;
        }else{
            randomArr(arr,num)
        }
    }
    function randomNumber() {
        return Math.floor(Math.random()*31 + 2)
    }

    var arr = new Array(5);
    var num = randomNumber();
    var i = 0;
    randomArr(arr,num);
    function randomArr(arr,num) {
        if (arr.indexOf(num)< 0){
            arr[i] = num;
            i++;
        } else {
            num = randomNumber();
        }
        if (i>=arr.length){
            console.log(arr);
            return;
        }else{
            randomArr(arr,num)
        }
    }
    function randomNumber() {
        return Math.floor(Math.random()*31 + 2)
    }

i++后面应该加一句num = randomNumber();不然每次重新赋值随机数都会占用一次递归.

from fe-interview.

这一题是起源题

描述：

1. 这是一道大题目，把考点拆成了4个小项；需要侯选人用递归算法实现（限制15行代码以内实现；限制时间10分钟内完成）：
   a) 生成一个长度为5的空数组arr。
   b) 生成一个（2－32）之间的随机整数rand。
   c) 把随机数rand插入到数组arr内，如果数组arr内已存在与rand相同的数字，则重新生成随机数rand并插入到arr内[需要使用递归实现，不能使用for/while等循环]
   d) 最终输出一个长度为5，且内容不重复的数组arr。

let arr = [];
function PushArr() {
let num = 2 + Math.floor(Math.random() * 30);
if (arr.length < 5) {
if (arr.indexOf(num) === -1) {
arr.push(num);
PushArr();
} else {
PushArr();
}
if (arr.length === 5) {
return arr;
}
}
}
PushArr();

from fe-interview.

var arr  = new Array(5),
      num  = Math.ceil(Math.random() * 31 + 1),
      i = 0;
  function randomArr(a,n){
    //去重
    if (a.indexOf(n) < 0){
      a[i] = n;
      i++;
    }else{
      n  = Math.ceil(Math.random() * 31 + 1);
    } 
    //递归条件
    if(i >= a.length){
      return;
    }else{
      randomArr(a,n);
    } 
  }
  randomArr(arr,num);

from fe-interview.

  var arr = new Array(5);//创建长度为5的空数组
      var rand,i = 0;//声明随机数rand和i
      function rDom(rand,i){
        rand = Math.round(Math.random()*30)+2; //生成2~32的整数
        if(arr[4] != undefined){ //递归结束条件
          return arr;
        }else{
          if(arr.indexOf(rand) == -1){ //indexOf检索arr数组
            arr[i] = rand;
            i++;
          }
          return rDom(rand,i);   
        }
      }
      rDom(rand,i); 
      console.log(arr);

from fe-interview.

let arr = []
for (let i = 0; i < 5; i++) {
function fn() {
let num = Math.floor(Math.random() * 30 + 2)
if (!arr.includes(num)) {
arr[i] = num
} else {
fn()
}
}
fn()
}
console.log(arr)

from fe-interview.

			function fillRandomNum(arr) {
				while (true) {
					// fixed interval random number
					//［a, b)：  (int)(Math.random()*(b-a)+a)
					//［a, b]：   (int)(Math.random()*(b-a+1)+a)
					var item = Math.floor(Math.random() * 30 + 2)
					if (arr.includes(item)) {
						++i
					} else {
						arr.push(item)
						return arr
					}
				}
			}
			function fillArray(arr) {
				debugger
				var array = arr || []
				if (
					array.filter(e => e < 2 || e >= 32).length > 0 &&
					array.length > 0
				)
					array = []
				if (array.length === 5) {
					return array
				} else {
					array = fillRandomNum(array)
					// here must return keyword that console the end array
					return fillArray(array)
				}
			}
			console.log(fillArray([1]))

from fe-interview.

let arr = [];
function generate() {
    if (arr.length < 5) {
        // 产生随机数
        let number = Math.ceil(Math.random() * 30 + 2);
        if (arr.indexOf(number) > -1) {
            generate();
        } else {
            arr.push(number);
            generate();
        }
    }
}
generate(); 
console.log('arr:', arr);

from fe-interview.

干好15行~~~

let arr = new Array(5);
let i = 0;
let rand = parseInt(Math.random() * 30 + 2);
let setArr = function (x) {
if (arr[arr.length - 1]) {
return arr;
};
if(arr.includes(x)) {
rand = parseInt(Math.random() * 30 + 2);
}else {
arr[i++] = rand
}
setArr(rand);
return arr;
}

from fe-interview.

const fn= function(n, r){
   if(!n){
     n = 0;
     r = [];
   }
  return n+1 <6 ? r.concat(Math.floor(Math.random()*31 + 2)).concat(fn(n+1, r)) : r;

}
fn();

from fe-interview.

var arr = [];
function fn (arr=[], length=5, min=2, max=32) {
	if (arr.length >= length 
		|| !Array.isArray(arr) 
		|| typeof length !== 'number'
		|| typeof min !== 'number'
		|| typeof max !== 'number'
		|| min > max){
		return;
	}
	length = length > max - min ? max - min : length;
	var val = Math.floor( Math.random() * (max - min + 1)  + min );
	if ( !arr.includes( val ) ) {
		arr.push(val);
	}
	fn(arr, length, min, max);
}
fn(arr);
console.log(arr);

from fe-interview.

 // ------优化includes indexOf 查找速度 ,避免这一项时间复杂度--------------

    // 使用 set 数组自动去重特性
    function getRandom(n) {
      var setArray = new Set();
      return function insert2(_setArray) {
        if (_setArray.size == n) {
          //最终返回时 将set 转为 普通数组格式 []
          return [..._setArray];
        }
        var number = parseInt(Math.random() * 31 + 2);
        // set 数组自动去重特性,避免了 每次查找数组是否有值
        _setArray.add(number);
        return insert2(_setArray);
      }(setArray)
    }
   getRandom(5)

from fe-interview.

考虑扩展性,可能有点性能问题~

function getArr(length,min,max){
    var arr=[],hash={};
    function fn(){
        var num=Math.floor(Math.random()*(max-1))+min;
        if(!hash[num]){
            hash[num] = true;
            arr.push(num);
        }
        return arr.length===length?arr:fn();
    }
    return fn();
}
getArr(5,2,32)

from fe-interview.

const fn = (arr = [], x) => {
  if(arr.length >= 5) { return arr }
  x && !arr. includes(x) && arr.push(x)
  return fn(arr, Math.floor((Math.random() * 32)) + 2) }
fn()

from fe-interview.

const varr = Array(5);
const rand1 = Math.max(2, Math.floor((Math.random() * 1000) % 32));
const vres = [];
function fillArr(arr, res) {
  const rand = Math.max(2, Math.floor((Math.random() * 1000) % 32));
  if (arr.indexOf(rand) == -1 && res.length < 5) {
    res.push(rand);
    arr.push(rand);
    fillArr(arr, res)
  } else if (res.length >= 5) {
    return res;
  }
}
fillArr(varr, vres);

主要学习到更优雅的随机数生成方法Math.floor(Math.random()*31+2) ~
另外没有使用下标，而是直接生成新数组，内部判断合并

from fe-interview.