Walmart Labs Coding Interview Questions

Longest Substring Without Repeating Characters

Given a string s, find the length of the longest substring without duplicate characters.

LRU Cache

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.

Valid Parentheses

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.

Merge Intervals

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cove...

Best Time to Buy and Sell Stock

You are given an array prices where prices[i] is the price of a given stock on the ith day.

Longest Palindromic Substring

Given a string s, return the longest palindromic substring in s.

Two Sum

Given an array of integers nums and an integer target, return the indices of the two numbers that add up to target.

Divide Intervals Into Minimum Number of Groups

You are given a 2D integer array intervals where intervals[i] = [lefti, righti] represents the inclusive interval [lefti, righti].

Word Break

Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words.

Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

Number of Ways to Separate Numbers

You wrote down many positive integers in a string called num. However, you realized that you forgot to add commas to seperate the different numbers. You remembe...

Minimum Operations to Make Array Equal II

You are given two integer arrays nums1 and nums2 of equal length n and an integer k. You can perform the following operation on nums1:

Count Good Triplets in an Array

You are given two 0-indexed arrays nums1 and nums2 of length n, both of which are permutations of [0, 1, ..., n - 1].

Minimum Number of Operations to Make Arrays Similar

You are given two positive integer arrays nums and target, of the same length.

Maximum Number of Tasks You Can Assign

You have n tasks and m workers. Each task has a strength requirement stored in a 0-indexed integer array tasks, with the ith task requiring tasks[i] strength to...

Middle of the Linked List

Given the head of a singly linked list, return the middle node of the linked list.

Spiral Matrix

Given an m x n matrix, return all elements of the matrix in spiral order.

Search in Rotated Sorted Array

There is an integer array nums sorted in ascending order (with distinct values).

Group Anagrams

Given an array of strings strs, group the anagrams together. You can return the answer in any order.

Number of Islands

Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.

Kth Largest Element in an Array

Given an integer array nums and an integer k, return the kth largest element in the array.

Longest Consecutive Sequence

Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.

Sort Colors

Given an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order...

Combination Sum

Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum...

Coin Change

You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money.

Valid Sudoku

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

Binary Tree Zigzag Level Order Traversal

Given the root of a binary tree, return the zigzag level order traversal of its nodes' values. (i.e., from left to right, then right to left for the next level...

Move Zeroes

Given an integer array nums, move all 0's to the end of it while maintaining the relative order of the non-zero elements.

Degree of an Array

Given a non-empty array of non-negative integers nums, the degree of this array is defined as the maximum frequency of any one of its elements.

3Sum

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.

Rotate Array

Given an integer array nums, rotate the array to the right by k steps, where k is non-negative.

Pow(x, n)

Implement pow(x, n), which calculates x raised to the power n (i.e., xn).

Median of Two Sorted Arrays

Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.

Top K Frequent Elements

Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.

All Nodes Distance K in Binary Tree

Given the root of a binary tree, the value of a target node target, and an integer k, return an array of the values of all nodes that have a distance k from the...

House Robber

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from rob...

Daily Temperatures

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait aft...

LFU Cache

Design and implement a data structure for a Least Frequently Used (LFU) cache.

Flatten Nested List Iterator

You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an...

Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

Merge k Sorted Lists

You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.

Copy List with Random Pointer

A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null.

Reverse Nodes in k-Group

Given the head of a linked list, reverse the nodes of the list k at a time, and return the modified list.

Search a 2D Matrix

You are given an m x n integer matrix matrix with the following two properties:

Add Binary

Given two binary strings a and b, return their sum as a binary string.

First Missing Positive

Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums.

Word Search

Given an m x n grid of characters board and a string word, return true if word exists in the grid.

Squares of a Sorted Array

Given an integer array nums sorted in non-decreasing order, return an array of the squares of each number sorted in non-decreasing order.

Minimum Window Substring

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is inc...

Maximum Subarray

Given an integer array nums, find the subarray with the largest sum, and return its sum.

Keys and Rooms

There are n rooms labeled from 0 to n - 1 and all the rooms are locked except for room 0. Your goal is to visit all the rooms. However, you cannot enter a locke...

Course Schedule II

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, b...

Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Binary Tree Right Side View

Given the root of a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Course Schedule

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, b...

Merge Two Sorted Lists

You are given the heads of two sorted linked lists list1 and list2.

Best Time to Buy and Sell Stock II

You are given an integer array prices where prices[i] is the price of a given stock on the ith day.

Populating Next Right Pointers in Each Node

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition:

Container With Most Water

You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i, 0) and (i, height[i]).

Subarray Sum Equals K

Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k.

Jump Game II

You are given a 0-indexed array of integers nums of length n. You are initially positioned at index 0.

Partition Equal Subset Sum

Given an integer array nums, return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false oth...

Path Sum II

Given the root of a binary tree and an integer targetSum, return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path...

First Unique Character in a String

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Max Consecutive Ones III

Given a binary array nums and an integer k, return the maximum number of consecutive 1's in the array if you can flip at most k 0's.

Wildcard Matching

Given an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '' where:

Koko Eating Bananas

Koko loves to eat bananas. There are n piles of bananas, the ith pile has piles[i] bananas. The guards have gone and will come back in h hours.

Interleaving String

Given strings s1, s2, and s3, find whether s3 is formed by an interleaving of s1 and s2.

Flatten Deeply Nested Array

Given a multi-dimensional array arr and a depth n, return a flattened version of that array.

Decode String

Given an encoded string, return its decoded string.

Second Highest Salary

Table: Employee

Largest Rectangle in Histogram

Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, return the area of the largest rectangle in the his...

Decode Ways

You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping:

Count Primes

Given an integer n, return the number of prime numbers that are strictly less than n.

Longest Palindrome

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters.

Maximal Square

Given an m x n binary matrix filled with 0's and 1's, find the largest square containing only 1's and return its area.

Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a sing...

Binary Tree Maximum Path Sum

A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequ...

Product of Array Except Self

Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].

Palindrome Number

Given an integer x, return true if x is a palindrome, and false otherwise.

Boats to Save People

You are given an array people where people[i] is the weight of the ith person, and an infinite number of boats where each boat can carry a maximum weight of lim...

Valid Palindrome II

Given a string s, return true if the s can be palindrome after deleting at most one character from it.

Linked List Cycle

Given head, the head of a linked list, determine if the linked list has a cycle in it.

Reverse Words in a String III

Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Valid Anagram

Given two strings s and t, return true if t is an anagram of s, and false otherwise.

Perfect Squares

Given an integer n, return the least number of perfect square numbers that sum to n.

Populating Next Right Pointers in Each Node II

Given a binary tree

Reorganize String

Given a string s, rearrange the characters of s so that any two adjacent characters are not the same.

Fruit Into Baskets

You are visiting a farm that has a single row of fruit trees arranged from left to right. The trees are represented by an integer array fruits where fruits[i] i...

Palindrome Partitioning

Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s.

Maximum Number of Non-overlapping Palindrome Substrings

You are given a string s and a positive integer k.

Minimum Add to Make Parentheses Valid

A parentheses string is valid if and only if:

Reverse Words in a String

Given an input string s, reverse the order of the words.

Merge Sorted Array

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and num...