List of some of the famous coding interview questions and their solutions.

1. Arrays

   1. Find Next Greater Element
   2. Find Pythagoras Triplets
   3. Find 3 items whose sum matches K
   4. Stock Span Problem
   5. Longest Increasing Subsequence
   6. Max Difference between two elements

2. 2D Arrays / Matrix

   1. Rotate Matrix by 90 degree

3. Numbers

   1. Fibonacci Series
   2. Find all prime numbers in a Range
   3. Find Missing numbers in Increasing sequence

4. Linked Lists

   1. Add 2 Numbers represented by Linked List
   2. Find the merging point of 2 linked lists
   3. Reverse a LinkedList in group

5. Set

   1. Create sets for given array

6. Strings

   1. First recurring character within a string
   2. Given a string, find all sub-strings which are Palindromes
   3. Replace char with word
   4. Find if 2 strings are Anagram

7. Write your own questions

   1. WYO - HashMap
   2. LRU Cache
   3. Fast DS

8. Tree

   1. Height of Binary Tree
   2. Tree Column Wise Sum
   3. Zig Zag Level order Traversal
   4. Check if 2 Binary trees are identical
   5. Binary Tree - Right View
   6. Binary Tree - Top View
   7. Binary Tree - Traversal
   8. Binary Tree - Level Order Traversal
   9. Binary Tree - Reverse Level Order Traversal
   10. Binary Tree to Sum Tree

NextGreaterElement - The Next greater Element for an element x is the first greater element on the right side of x in array. Elements for which no greater element exist, consider next greater element as -1.

PythagorasTriplets - Given an array, find if it contains the Pythagoras Triplets. Triplet (a,b,c) such that a^2 + b^2 = c^2.

Three Sum Problem - Given an array and a value, find if there is a triplet in array whose sum is equal to the given value.

StockSpan - https://www.geeksforgeeks.org/the-stock-span-problem/

LongestIncreasingSubsequence - https://www.interviewbit.com/problems/longest-increasing-subsequence/. Find the number of elements in the longest increasing subsequence.

Maximum Difference between two elements - https://www.geeksforgeeks.org/maximum-difference-between-two-elements/ - Maximum difference between two elements such that larger element appears after the smaller number.

RotateMatrixBy90Degree - Given a n * n matrix, rotate its element by 90 degrees.

FibonacciSeries (Dynamic Programming) - Find Fibonacci series upto N.

FindAllPrimeNumbersInRange - Find all prime numbers in a given range (N, M)

FindMissingNumbersInIncreasingArray - Given an array which has numbers from [1...N] find the missing number.

Add2NumbersRepresentedByLL - Given two numbers represented by two lists, write a function that returns sum list. The sum list is list representation of addition of two input numbers.

MergingPointOf2Liists - Given the pointers to the head node of 2 lists which will surely merge, find the merging point (node), at which they merge.

ReverseLinkedListInGroup - Reverse Linked List within a group of k elements. For example, if the list is 1 -> 2 -> 3 -> 4 -> 5 ->6 -> 7 and k = 3, then output list will be 3 -> 2 -> 1 -> 6 -> 5 -> 4 -> 7.

SetForGivenArray - Create set consisting of all the possible combinations of elements, for a given array.

FirstRecurringCharacter - Find the first recurring character within a given string.

AllSubstringPalindromes - Given a string, find all the substrings of that string which are palindrome

ReplaceACharWithAWord - Replace a single char of a String, with a word (String replace without using Java built-in functions)

TwoStringAnagram - Find of 2 strings are Anagrams

"Write your own" interview questions, tests your ability of understanding a particular concept or data structure.

HashMap - HashMap is a hash based Key-Value pair data structure, which will give O(1) time complexity for put and get operations. "Write-your-own" HashMap is a famous Java data structure based interview question to understand, how deep you know about this famous data structure.

LRUCache - LRU Cache - is a key-value pair, which is of fixed length. Whenever the capacity of the cache reaches to MAX, then it evicts the "Least Recently Used" key.

FastDS - A custom data structure, which performs add, delete, get and getRandom() operation @ O(n) complexity

HeightOfBinaryTree - is a recursive way of finding the height of a binary tree (height of binary tree - max (height of left sub-tree, height of right sub-tree)

Column Wise Sum of Binary Tree - Column wise sum of binary tree

Zig Zag Traversal on Binary Tree - Zig Zag traversal on binary tree (level order) using 2 stacks

Check if 2 binary trees are identical - Using recursion to find out if 2 binary trees are identical

RightView - Right view of the Binary Tree

TopView - Top view of the Binary Tree

Traversal - All 3 traversals of Binary Tree (Inorder, Preorder and Postorder)

LevelOrderTraversal - Level order Traversal of the Binary Tree

ReverseLevelOrderTraversal - Reverse Level order Traversal of the Binary Tree

BinartTreeToSumTree - Binary tree to the sum tree problem. Each parent node will have a value = cumulative (left node value + right node value)