Leetcode Leetcode Premium vs Lintcode VIP Leetcode, Lintcode, Hackerrank, Hackerearth and Interviewbit are some of the leading preparation platforms. Of all these, Leetcode is the most famous one because of its vast collection of questions and a company focussed preparation style.

Leetcode Medium Longest Palindromic Substring Java Problem Statement Given a string, Find the longest palindromic substring. Solution Explanation Understanding the question here is very simple, given a string RENTNOW, the substring NTN is a palindrome of length 3, and

Leetcode Easy Balanced Parentheses Validation - Java Problem Statement Given an string or expression which only consists of characters like (, ), [, ], {, } . Validate if the string has balanced parentheses. A string has balanced parentheses, if every open bracket has an associated closed

Frequently Asked Questions Calculate the Hamming Distance between two Integers Problem Statement Given two integers, calculate the hamming distance between them. Solution Explanation Hamming Distance between integers is defined as the number of indexes where the two bits differ. For example, given integers

Data Structures Doubly Linked List Implementation Java LinkedList is a linear data structure which allows to insert and remove elements at the front and rear in constant time. LinkedLists are typically of two types, Single LinkedList Each node has a

Data Structures Introduction to Queue and Implementation using Linked List Queue is a linear datastructure that stores elements with first in first out(FIFO) ordering. That is, the element which gets added to the queue leaves before all the elements added after it.

Data Structures Stack Implementation using Single LinkedList Java Stack is one of the most used data structures in computer science. It is a linear data structure which supports ordering of elements in Last In First Out order(LIFO). The very typical

Array Trapping Rain Water Solution Java Problem Statement Given an a list of n integers which are non negative and represent an elevation map of various buildings where the width of each bar/building is 1, Find out how

Array Find K Pairs with Smallest Sum Java Solution Problem Statement Given two integer arrays, arr1 and arr2, find K pairs of elements such that (x,y) where x is the value from the first array and y is the value from

Array Find Two Numbers in an Array Which Sum Up to K Problem Statement Given an array of integers, find out two indices such that the sum of the numbers at that indices matches K. For example, {4, 6, 8, 1, 9} and K = 15,

Array Check If a Sudoku is Valid Problem Statement Determine if a sudoku is Valid. Solution Explanation Given a sudoku grid, we need to verify if the already filled in numbers doesn't violate the sudoku rules. The rules are very

Math Generate all Factor Combinations Problem Statement Given a number 'n', generate all factor combinations. For example, when n=24, the result would be [[2, 3, 3], [2, 9], [3, 6]] Solution Explanation As we know, every integer

Linked List Check if a LinkedList has a cycle Problem Statement Given a single linked list, verify if the list has a cycle. A linked list has a cycle if a node's reference points back to an earlier node in the chain.

Array Best Time to Buy and Sell Stock Problem Statement Given an array 'stocks' in which each value at index 'i' is the stock price on day 'i', Find the maximum profit you can make by performing atmost one Buy and

Leetcode Medium Find Inorder Successor in a Binary Search Tree Problem Statement Given a binary search tree and the value of a certain node, find the next node in the inorder sequence after the given node. Solution Explanation The important information here is

Linked List Linked List Implementation Java Problem Statement Implement a single linked list in Java Solution Explanation Linked List is one of the heavily used data structure in computer programming. It is basically a linear collection of data elements

Array Number of Islands Leetcode Problem Statement Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or

Math Find the Celebrity Problem Statement Suppose you are at a party with n people (labeled from 0 to n - 1) and among them, there may exist one celebrity. The definition of a celebrity is that

Array Three Sum(3Sum) Leetcode Problem Statement Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the

Array Meeting Rooms Leetcode Problem Statement Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), find the minimum number of conference rooms required. For example, Given

String Decode Ways Leetcode Problem Statement A message containing letters from A-Z is being encoded to numbers using the following mapping: 'A' -> 1 'B' -> 2 ... 'Z' -> 26 Given an encoded message

String Letter Combinations of a Phone Number Problem Statement Given a digit string, return all possible letter combinations that the number could represent. Input:Digit string "23" Output: ["ad", "ae", "af", "

Interview Questions Add Binary Leetcode Problem Statement Given two binary strings, return their sum (also a binary string). For example,a = "11", b = "1" Return "100". Solution Explanation The question is very

Binary Tree Binary Tree Vertical Order Traversal Leetcode Problem Statement Given a binary tree, return the vertical order traversal of its nodes' values. (ie, from top to bottom, column by column). Solution Explanation Given a binary tree, 35 / \ 23 27 / \ \ 14

Array Sparse Matrix Multiplication Problem Statement Given two sparse matrices A and B, return the result of AB. You may assume that A's column number is equal to B's row number. Solution Explanation A sparse matrix is