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Technical Interview Questions and Solutions

Browse our database of interview questions and full-length solutions from top companies
HARD
Data Structures and Algorithms
Given an array Z of 0s and 1s, divide the array into 3 non-empty parts, such that all of these parts represent the same binary value.
MEDIUM
Data Structures and Algorithms
Given a list of file paths, print all of the files in each of the folders.
MEDIUM
System Design
Create a service that allows users to upload an image and apply filters and then sends users a link to download their filtered image.
MEDIUM
Data Structures and Algorithms
Given two strings s1 and s2, return true if s2 contains a permutation of s1, or false otherwise.
MEDIUM
Data Structures and Algorithms
Given an integer array nums, find the subarray with the largest sum, and return its sum.
MEDIUM
Data Structures and Algorithms
Given an array of integers, transform the array in-place to a max heap.
MEDIUM
Data Structures and Algorithms
Given a two-dimensional binary matrix where 1 represents water and 0 represents land, mutate the matrix in place and return the matrix with the highest peak maximized.
MEDIUM
Data Structures and Algorithms
You are given a path to a file as a string. The path can contain the symbols: “..” for the parent directory and “.” for the current directory. Convert the path into its simplified form.
MEDIUM
Data Structures and Algorithms
Given an unsorted array of integers and an integer k, find the number of subarrays whose sum equals k.
MEDIUM
Data Structures and Algorithms
Given a string s, find the length of the longest substring without repeating characters.
MEDIUM
System Design
How would you organize a SQL database like MySQL such that you can add more machines once your current ones reach maximum capacity? With the limitation that you do not have access to any automated tools for distributing.
MEDIUM
Data Structures and Algorithms
Given the head of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return the reordered list.
MEDIUM
Data Structures and Algorithms
Given `n` pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
MEDIUM
Data Structures and Algorithms
Design and implement an efficient sampler that works in average O(1) time complexity.
MEDIUM
Data Structures and Algorithms
Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure.
MEDIUM
Data Structures and Algorithms
Given a tree, verify that on even levels, all values in the level are strictly increasing and even. On odd levels, verify all values in the level are strictly decreasing and odd.
MEDIUM
Data Structures and Algorithms
Given the head of a linked list, remove the nth node from the end of the list and return its head.
MEDIUM
Data Structures and Algorithms
Given an array of employee IDs including who they report to, write a function to calculate the score for a given employee.
MEDIUM
Data Structures and Algorithms
Given an integer array and an integer k, return the kth smallest element in the array.
MEDIUM
Data Structures and Algorithms
Given an array of integers, return an array of triplets such that i != j != k and nums[i] + nums[j] + nums[k] = 0.
MEDIUM
Data Structures and Algorithms
You are given a m x n 2D grid initialized with these three possible values. Fill each empty room with the distance to its nearest gate.
EASY
System Design
Given an inefficient file structure, how would you store data to efficiently look up the query? How would you alter this if you had many computers available?
HARD
Data Structures and Algorithms
Given the head of a linked list, reverse the nodes of the list k at a time, and return the modified list.
EASY
Data Structures and Algorithms
Print out all 8-digit palindromes. Limitation: We can't use string manipulation.
EASY
Data Structures and Algorithms
Determine if this string, after removing any one character, can become a palindrome. If possible return true, otherwise return false.
MEDIUM
Data Structures and Algorithms
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.
MEDIUM
Data Structures and Algorithms
Given a sequence of fruit trees represented as an array of strings. Return the maximum number of fruit trees you can pick from given you can only have one type of fruit in each basket and once you start picking you can't skip a tree and then keep picking.
EASY
Data Structures and Algorithms
Given the head of a linked list, reverse the list and return the new head.
MEDIUM
Data Structures and Algorithms
Given an encoded string, return its decoded string.
MEDIUM
Data Structures and Algorithms
Given a set of parameters, find the conversion rate that maps to the 'from' currency to the 'to' currency from every single query. Your return value should be a number.
MEDIUM
Data Structures and Algorithms
Given the root of a complete binary tree, return the number of nodes in the tree.
MEDIUM
Data Structures and Algorithms
Write an XML parser and formatter.
MEDIUM
Data Structures and Algorithms
Implement an LRU Cache LRU = Least recently used cache
MEDIUM
Data Structures and Algorithms
You are given the root of a binary tree containing digits from 0 to 9 only. Each root-to-leaf path in the tree represents a number, for example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123. Return the total sum of all root-to-leaf numbers.
MEDIUM
Data Structures and Algorithms
Given a list of integers L and a number K, write a function that reorganizes L into three partitions: elements less than K, elements equal to K, and elements greater than K. No additional lists may be used.
EASY
Data Structures and Algorithms
Given an input string `s`, reverse the order of the words without reversing the words themselves.
MEDIUM
Data Structures and Algorithms
Given a linked list with nodes that have an additional pointer referring to another node in the list, return a deep copy of the list.
MEDIUM
Data Structures and Algorithms
Given two strings, return the longest common subsequence between the two strings.
MEDIUM
Data Structures and Algorithms
Given n non-negative integers, find two lines that form a container that can hold the most amount of water.
MEDIUM
Data Structures and Algorithms
Write an efficient program for printing k largest elements in an array. Largest elements are returned in order largest to smallest.
MEDIUM
Data Structures and Algorithms
Given an integer array nums and two integers left and right, return the number of contiguous non-empty subarrays such that the value of the maximum array element in that subarray is in the range [left, right].
MEDIUM
Data Structures and Algorithms
Write a function that takes a string as an input and returns a shuffled version of that string then write another function to analyze how well it was shuffled.
MEDIUM
Data Structures and Algorithms
Given an array of positive numbers, determine if the array can be split such that the two partition sums are equal.
MEDIUM
Data Structures and Algorithms
Given an integer array nums and an integer k, return true if it is possible to divide this array into k non-empty subsets whose sums are all equal.
MEDIUM
Data Structures and Algorithms
Given a string s, return the longest palindromic substring in s.
MEDIUM
Data Structures and Algorithms
Given an integer as an input, replace all the digits ‘0’ with ‘5’ in the integer.
MEDIUM
Data Structures and Algorithms
Write a function that, given a room with 800 BIDDERS, identifies all the confusable numbers.
HARD
System Design
Design a message app system and client (e.g. WhatsApp) supporting a list of requirements.
MEDIUM
Data Structures and Algorithms
Given a binary tree where every node has either 0 or 2 children and every right node is a leaf node, flip it upside down turning it into a binary tree where all left nodes are leaf nodes.
EASY
Data Structures and Algorithms
Given an m x n matrix of distinct numbers, return all lucky numbers in the matrix in any order.
MEDIUM
Data Structures and Algorithms
Given a string, find the length of the longest substring in it with no more than K distinct characters.
EASY
Data Structures and Algorithms
Given the heads of two singly linked-lists headA and headB, return the node at which the two lists intersect.
HARD
Data Structures and Algorithms
Given an input string (s) and a pattern (p), implement regular expression matching with support for '.' and '*'. '.' Matches any single character. '*' Matches zero or more of the preceding element.
MEDIUM
System Design
Design the service for an app that supports distributing 6 million burgers in 10 minutes.
MEDIUM
Data Structures and Algorithms
Given a list of words, match all words with other words from the list that are a prefix for the word.
MEDIUM
Data Structures and Algorithms
Given a 2-D integer array mapping the letters ABCD and their costs. Calculate the smallest cost to make a string of length n.
EASY
Data Structures and Algorithms
Print out all numbers in binary, preserving leading zeros.
MEDIUM
Given a binary tree, extract all the leaves in repeated succession into a list of lists by starting at the bottom and working your way upwards.
MEDIUM
Data Structures and Algorithms
Given a non-empty array of integers, return the k most frequent elements.
MEDIUM
Mathematics
Given a 32-bit signed integer, reverse digits of the integer.
EASY
Data Structures and Algorithms
Given an array of integers, return the indices of the two numbers that add up to a given target.
MEDIUM
Data Structures and Algorithms
Given an array of integers, find the most frequent element in the array. Write a method that takes an array of integers and returns an integer. If there is a tie, you can just return any.
MEDIUM
Data Structures and Algorithms
Given a 2D matrix, where "1" represents land and "0" represents water, count how many islands are present.
MEDIUM
Data Structures and Algorithms
The boundary of a binary tree is the concatenation of the root, the left boundary, the leaves ordered from left-to-right, and the reverse order of the right boundary.
HARD
Data Structures and Algorithms
You are given a list of lexicographically sorted words from an alien language. This language has a unique order. Return the alphabetical order of all the letters found in the list of words.
HARD
Data Structures and Algorithms
Given a dictionary of words, determine whether it is possible to transform a given word into another with a fixed number of characters.
HARD
Data Structures and Algorithms
Given an integer array nums and an integer k, split nums into k non-empty subarrays such that the largest sum of any subarray is minimized. Return the minimized largest sum of the split.
HARD
Data Structures and Algorithms
Given an m x n integers matrix, return the length of the longest increasing path in the matrix. You may only move up, down, left, or right.
MEDIUM
Data Structures and Algorithms
Given an unsorted array of unique integers (size n + 1) and a first array identical to the second array, missing one integer (size n), find and output the missing integer.
HARD
System Design
Design a coding competition platform with a leaderboard and execution environment.
EASY
Data Structures and Algorithms
Write a program to reverse the given string.
MEDIUM
Data Structures and Algorithms
Given a list of meetings, represented as tuples with a start and an end time, determine the minimum number of rooms required to schedule all the meetings.
HARD
Data Structures and Algorithms
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 included in the window.
MEDIUM
Data Structures and Algorithms
Given a list of tuples that represent (X, Y) coordinates on an XY plane and an integer K, return a list of the K-closest points to the origin (0, 0).

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