Technical Interview Questions and Solutions

Browse our database of interview questions and full-length solutions from top companies

MEDIUM
Data Structures and Algorithms
Build a Max Heap

Given an array of integers, transform the array in-place to a max heap.

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MEDIUM
Data Structures and Algorithms
Three Sum

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

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EASY
Data Structures and Algorithms
Reverse Linked List

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

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MEDIUM
Data Structures and Algorithms
Container With Most Water

Given n non-negative integers, find two lines that form a container that can hold the most amount of water.

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EASY
Data Structures and Algorithms
Reverse String

Write a program to reverse the given string.

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EASY
Data Structures and Algorithms
Two Sum

Given an array of integers, return the indices of the two numbers that add up to a given target.

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MEDIUM
Mathematics
Reverse Integer

Given a 32-bit signed integer, reverse digits of the integer.

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MEDIUM
Data Structures and Algorithms
Find Peak Element

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
Meeting Rooms

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.

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MEDIUM
Data Structures and Algorithms
Recover Binary Search Tree

Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure.

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MEDIUM
Data Structures and Algorithms
Simplify Path

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
Count Complete Tree Nodes

Given the root of a complete binary tree, return the number of nodes in the tree.

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MEDIUM
Data Structures and Algorithms
Boundary of Binary Tree

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.

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MEDIUM
Data Structures and Algorithms
Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent elements

MEDIUM
Data Structures and Algorithms
K Closest Points To Origin

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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MEDIUM
Data Structures and Algorithms
Subarray Sum Equals K

Given an unsorted array of integers and an integer k, find the number of subarrays whose sum equals k.

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MEDIUM
Data Structures and Algorithms
Kth Smallest Element

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

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MEDIUM
Data Structures and Algorithms
Decode String

Given an encoded string, return its decoded string.

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MEDIUM
Data Structures and Algorithms
Generate Parentheses

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

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EASY
Data Structures and Algorithms
Reverse Words in a String

Given an input string `s`, reverse the order of the words without reversing the words themselves.

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MEDIUM
Data Structures and Algorithms
Longest Common Subsequence

Given two strings, return the longest common subsequence between the two strings.

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MEDIUM
Data Structures and Algorithms
Copy List With Random Pointers

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.

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MEDIUM
Find Leaves of Binary Tree

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.

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HARD
Data Structures and Algorithms
Alien Dictionary

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.

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MEDIUM
Data Structures and Algorithms
Right View Of Binary Tree

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.

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MEDIUM
Data Structures and Algorithms
Insert Delete getRandom O(1)

Design and implement an efficient sampler that works in average O(1) time complexity.

MEDIUM
Data Structures and Algorithms
Partition to K Equal Sum Subsets

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.

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MEDIUM
Data Structures and Algorithms
Partition List

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.

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MEDIUM
Data Structures and Algorithms
Number of Islands

Given a 2D matrix, where "1" represents land and "0" represents water, count how many islands are present.

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MEDIUM
Data Structures and Algorithms
Longest Substring Without Repeating Characters

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

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MEDIUM
Data Structures and Algorithms
Find Missing Number In Array (Two Arrays)

Given an unsorted array of unique integers (size n + 1) and a first array identical to the second array but missing one integer (size n), find and output the missing integer.

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