✅34. 在排序数组中查找元素的第一个和最后一个位置 about like-algorithms HOT 2 OPEN

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
    let first = -1;
    let last = -1;
    for (let i = 0; i < nums.length; i++) {
        if (target === nums[i]) {
            if (first === -1) {
                first = i;
            }
            last = i
        }
    }
    return [first, last];
};

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
    let left = binarySearch(nums, target, true);
    let right = binarySearch(nums, target, false) - 1;
    if (left <= right && right < nums.length && nums[left] === target && nums[right] === target) {
        return [left, right];
    }
    return [-1, -1];
};

function binarySearch(nums, target, lower) {
    let left = 0;
    let right = nums.length - 1;
    let ans = nums.length;
    while (left <= right) {
        const mid = Math.floor((left + right) / 2);
        if (nums[mid] > target || (lower && nums[mid] >= target)) {
            right = mid - 1;
            ans = mid;
        } else {
            left = mid + 1
        }
    }
    return ans;
}