PayPal Coding Interview Questions

Zigzag Conversion

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better...

LRU Cache

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

Count the Number of Vowel Strings in Range

You are given a 0-indexed array of string words and two integers left and right.

Count Vowel Strings in Ranges

You are given a 0-indexed array of strings words and a 2D array of integers queries.

Minimum Replacements to Sort the Array

You are given a 0-indexed integer array nums. In one operation you can replace any element of the array with any two elements that sum to it.

Number of Valid Move Combinations On Chessboard

There is an 8 x 8 chessboard containing n pieces (rooks, queens, or bishops). You are given a string array pieces of length n, where pieces[i] describes the typ...

Maximum Number of Integers to Choose From a Range I

You are given an integer array banned and two integers n and maxSum. You are choosing some number of integers following the below rules:

Time Needed to Rearrange a Binary String

You are given a binary string s. In one second, all occurrences of "01" are simultaneously replaced with "10". This process repeats until no occurrences of "01"...

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.

Word Search

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

Minimum Non-Zero Product of the Array Elements

You are given a positive integer p. Consider an array nums (1-indexed) that consists of the integers in the inclusive range [1, 2p - 1] in their binary represen...

Maximum Sum Obtained of Any Permutation

We have an array of integers, nums, and an array of requests where requests[i] = [starti, endi]. The ith request asks for the sum of nums[starti] + nums[starti...

Count Array Pairs Divisible by K

Given a 0-indexed integer array nums of length n and an integer k, return the number of pairs (i, j) such that:

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.

Group Anagrams

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

Paint House III

There is a row of m houses in a small city, each house must be painted with one of the n colors (labeled from 1 to n), some houses that have been painted last 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.

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.

Longest Increasing Subsequence

Given an integer array nums, return the length of the longest strictly increasing subsequence.

Coin Change

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

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].

Pairs of Songs With Total Durations Divisible by 60

You are given a list of songs where the ith song has a duration of time[i] seconds.

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...

Longest Substring Without Repeating Characters

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

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.

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...

Minimum Absolute Difference

Given an array of distinct integers arr, find all pairs of elements with the minimum absolute difference of any two elements.

Maximum Number of Events That Can Be Attended

You are given an array of events where events[i] = [startDayi, endDayi]. Every event i starts at startDayi and ends at endDayi.

Find the Smallest Divisor Given a Threshold

Given an array of integers nums and an integer threshold, we will choose a positive integer divisor, divide all the array by it, and sum the division's result....

Reorganize String

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

Loud and Rich

There is a group of n people labeled from 0 to n - 1 where each person has a different amount of money and a different level of quietness.

Meeting Rooms III

You are given an integer n. There are n rooms numbered from 0 to n - 1.

Last Stone Weight

You are given an array of integers stones where stones[i] is the weight of the ith stone.

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.

Count Vowel Substrings of a String

A substring is a contiguous (non-empty) sequence of characters within a string.

Valid Anagram

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

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.

Valid Parentheses

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

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...

Random Pick with Weight

You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index.

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...

Flatten Deeply Nested Array

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

Kth Largest Element in an Array

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

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.

Happy Number

Write an algorithm to determine if a number n is happy.

Maximum Subarray

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

Find First and Last Position of Element in Sorted Array

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

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.

Reverse Linked List

Given the head of a singly linked list, reverse the list, and return the reversed list.

Palindromic Substrings

Given a string s, return the number of palindromic substrings in it.

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.

Search in Rotated Sorted Array

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

Jump Game

You are given an integer array nums. You are initially positioned at the array's first index, and each element in the array represents your maximum jump length...

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:

Text Justification

Given an array of strings words and a width maxWidth, format the text such that each line has exactly maxWidth characters and is fully (left and right) justifie...

Count and Say

The count-and-say sequence is a sequence of digit strings defined by the recursive formula:

Subarray Product Less Than K

Given an array of integers nums and an integer k, return the number of contiguous subarrays where the product of all the elements in the subarray is strictly le...

Longest Consecutive Sequence

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

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.

LFU Cache

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

Minimum Increment to Make Array Unique

You are given an integer array nums. In one move, you can pick an index i where 0 <= i < nums.length and increment nums[i] by 1.

Minimum Number of Swaps to Make the String Balanced

You are given a 0-indexed string s of even length n. The string consists of exactly n / 2 opening brackets '[' and n / 2 closing brackets ']'.

Rotate Image

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

Minimum Number of Removals to Make Mountain Array

You may recall that an array arr is a mountain array if and only if:

Merge In Between Linked Lists

You are given two linked lists: list1 and list2 of sizes n and m respectively.

Maximum Product Subarray

Given an integer array nums, find a subarray that has the largest product, and return the product.

Design Twitter

Design a simplified version of Twitter where users can post tweets, follow/unfollow another user, and is able to see the 10 most recent tweets in the user's new...

Path Sum

Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path such that adding up all the values along the path equa...

Maximum Frequency Stack

Design a stack-like data structure to push elements to the stack and pop the most frequent element from the stack.

Number of Substrings Containing All Three Characters

Given a string s consisting only of characters a, b and c.

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.

Divide Players Into Teams of Equal Skill

You are given a positive integer array skill of even length n where skill[i] denotes the skill of the ith player. Divide the players into n / 2 teams of size 2...

Flatten Binary Tree to Linked List

Given the root of a binary tree, flatten the tree into a "linked list":

Delete Node in a Linked List

There is a singly-linked list head and we want to delete a node node in it.

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...

Word Search II

Given an m x n board of characters and a list of strings words, return all words on the board.

Process Tasks Using Servers

You are given two 0-indexed integer arrays servers and tasks of lengths n​​​​​​ and m​​​​​​ respectively. servers[i] is the weight of the i​​​​​​th​​​​ server,...

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.

Maximum Profit in Job Scheduling

We have n jobs, where every job is scheduled to be done from startTime[i] to endTime[i], obtaining a profit of profit[i].

Find Median from Data Stream

The median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value, and the median is the mean of the two midd...

Find Pivot Index

Given an array of integers nums, calculate the pivot index of this array.

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...

First Missing Positive

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

Jump Game II

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

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]).

Find Peak Element

A peak element is an element that is strictly greater than its neighbors.

Spiral Matrix

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

Lexicographically Smallest Palindrome

You are given a string s consisting of lowercase English letters, and you are allowed to perform operations on it. In one operation, you can replace a character...

Maximum Population Year

You are given a 2D integer array logs where each logs[i] = [birthi, deathi] indicates the birth and death years of the ith person.

Find Minimum in Rotated Sorted Array

Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example, the array nums = [0,1,2,4,5,6,7] might become:

Search a 2D Matrix II

Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties:

Invalid Transactions

A transaction is possibly invalid if:

Intersection of Two Arrays

Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must be unique and you may return the result in any...

Min Stack

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