Top 100 Interview Questions

Essential collection of 100 coding problems that appear most often in technical interviews.

100

Total Problems

20

Easy

62

Medium

18

Hard

83%

Avg Frequency

Most Common Topics

Array (52)Hash Table (25)String (25)Sorting (19)Dynamic Programming (15)Depth-First Search (15)Two Pointers (15)Heap (Priority Queue) (13)

Companies Asking These Questions

Meta (24)DoorDash (10)Google (8)Amazon (8)Microsoft (8)LinkedIn (8)

Problems in This Collection

#1EasyFrequency: 100%High Priority

Two Sum

Asked at Google

Array Hash Table

#1

Rank

#3594MediumFrequency: 100%High Priority

Identify the Largest Outlier in an Array

Asked at Amazon

Array Hash Table Counting Enumeration

#2

Rank

#3655MediumFrequency: 100%High Priority

Digit Operations to Make Two Integers Equal

Asked at Microsoft

Math Graph Heap (Priority Queue)Number Theory Shortest Path

#3

Rank

#1371MediumFrequency: 100%High Priority

Minimum Remove to Make Valid Parentheses

#4

Rank

#3638HardFrequency: 100%High Priority

Minimum Operations to Make Character Frequencies Equal

Asked at TikTok

Hash Table String Dynamic Programming Counting Enumeration

#5

Rank

#3613MediumFrequency: 100%High Priority

Maximize Amount After Two Days of Conversions

Array String Depth-First Search Breadth-First Search Graph

#6

Rank

#716HardFrequency: 100%High Priority

Max Stack

Asked at LinkedIn

Linked List Stack Design Doubly-Linked List Ordered Set

#7

Rank

#49MediumFrequency: 100%High Priority

Group Anagrams

Asked at Oracle

Array Hash Table String Sorting

#8

Rank

#71MediumFrequency: 100%High Priority

Simplify Path

Asked at Oracle

#9

Rank

#1306EasyFrequency: 100%High Priority

Minimum Absolute Difference

Asked at Oracle

#10

Rank

#532MediumFrequency: 100%High Priority

K-diff Pairs in an Array

Asked at Salesforce

Array Hash Table Two Pointers Binary Search Sorting

#11

Rank

#1423MediumFrequency: 100%High Priority

Maximum Number of Occurrences of a Substring

Asked at Salesforce

Hash Table String Sliding Window

#12

Rank

#286MediumFrequency: 100%High Priority

Walls and Gates

Asked at DoorDash

Array Breadth-First Search Matrix

#13

Rank

#1171MediumFrequency: 100%High Priority

Shortest Path in Binary Matrix

Asked at Airbnb

Array Breadth-First Search Matrix

#14

Rank

#146MediumFrequency: 100%High Priority

LRU Cache

Asked at Flipkart

Hash Table Linked List Design Doubly-Linked List

#15

Rank

#295HardFrequency: 100%High Priority

Find Median from Data Stream

Asked at PayPal

Two Pointers Design Sorting Heap (Priority Queue)Data Stream

#16

Rank

#362MediumFrequency: 100%High Priority

Design Hit Counter

Asked at Databricks

Array Binary Search Design Queue Data Stream

#17

Rank

#314MediumFrequency: 97%High Priority

Binary Tree Vertical Order Traversal

Hash Table Tree Depth-First Search Breadth-First Search Sorting+1 more

#18

Rank

#227MediumFrequency: 96%High Priority

Basic Calculator II

Math String Stack

#19

Rank

#658MediumFrequency: 96%High Priority

Find K Closest Elements

Asked at DoorDash

Array Two Pointers Binary Search Sliding Window Sorting+1 more

#20

Rank

#680EasyFrequency: 95%High Priority

Valid Palindrome II

Two Pointers String Greedy

#21

Rank

#833HardFrequency: 95%High Priority

Bus Routes

Array Hash Table Breadth-First Search

#22

Rank

#348MediumFrequency: 93%High Priority

Design Tic-Tac-Toe

Asked at Databricks

Array Hash Table Design Matrix Simulation

#23

Rank

#88EasyFrequency: 92%High Priority

Merge Sorted Array

Asked at Microsoft

Array Two Pointers Sorting

#24

Rank

#215MediumFrequency: 92%High Priority

Kth Largest Element in an Array

Array Divide and Conquer Sorting Heap (Priority Queue)Quickselect

#25

Rank

#1790MediumFrequency: 91%High Priority

Lowest Common Ancestor of a Binary Tree III

Hash Table Two Pointers Tree Binary Tree

#26

Rank

#364MediumFrequency: 88%High Priority

Nested List Weight Sum II

Asked at LinkedIn

Stack Depth-First Search Breadth-First Search

#27

Rank

#1046MediumFrequency: 88%High Priority

Max Consecutive Ones III

Asked at LinkedIn

Array Binary Search Sliding Window Prefix Sum

#28

Rank

#200MediumFrequency: 88%High Priority

Number of Islands

Asked at Salesforce

Array Depth-First Search Breadth-First Search Union Find Matrix

#29

Rank

#300MediumFrequency: 88%High Priority

Longest Increasing Subsequence

Asked at Salesforce

Array Binary Search Dynamic Programming

#30

Rank

#460HardFrequency: 88%High Priority

LFU Cache

Asked at Salesforce

Hash Table Linked List Design Doubly-Linked List

#31

Rank

#647MediumFrequency: 88%High Priority

Palindromic Substrings

Asked at Salesforce

Two Pointers String Dynamic Programming

#32

Rank

#408EasyFrequency: 87%High Priority

Valid Word Abbreviation

Two Pointers String

#33

Rank

#912MediumFrequency: 87%High Priority

Random Pick with Weight

Array Math Binary Search Prefix Sum Randomized

#34

Rank

#125EasyFrequency: 87%High Priority

Valid Palindrome

Asked at Oracle

Two Pointers String

#35

Rank

#206EasyFrequency: 87%High Priority

Reverse Linked List

Asked at Oracle

Linked List Recursion

#36

Rank

#238MediumFrequency: 87%High Priority

Product of Array Except Self

Asked at Oracle

Array Prefix Sum

#37

Rank

#322MediumFrequency: 87%High Priority

Coin Change

Asked at Oracle

Array Dynamic Programming Breadth-First Search

#38

Rank

#1478MediumFrequency: 87%High Priority

Maximum Number of Events That Can Be Attended

Asked at Oracle

Array Greedy Sorting Heap (Priority Queue)

#39

Rank

#621MediumFrequency: 85%High Priority

Task Scheduler

Asked at Amazon

Array Hash Table Greedy Sorting Heap (Priority Queue)+1 more

#40

Rank

#50MediumFrequency: 85%High Priority

Pow(x, n)

#41

Rank

#162MediumFrequency: 85%High Priority

Find Peak Element

Array Binary Search

#42

Rank

#3MediumFrequency: 84%High Priority

Longest Substring Without Repeating Characters

Asked at Microsoft

Hash Table String Sliding Window

#43

Rank

#339MediumFrequency: 84%High Priority

Nested List Weight Sum

Depth-First Search Breadth-First Search

#44

Rank

#366MediumFrequency: 84%High Priority

Find Leaves of Binary Tree

Asked at LinkedIn

Tree Depth-First Search Binary Tree

#45

Rank

#8MediumFrequency: 84%High Priority

String to Integer (atoi)

Asked at Databricks

#46

Rank

#198MediumFrequency: 84%High Priority

House Robber

Asked at Databricks

Array Dynamic Programming

#47

Rank

#213MediumFrequency: 84%High Priority

House Robber II

Asked at Databricks

Array Dynamic Programming

#48

Rank

#752MediumFrequency: 84%High Priority

IP to CIDR

Asked at Databricks

String Bit Manipulation

#49

Rank

#124HardFrequency: 83%High Priority

Binary Tree Maximum Path Sum

Asked at DoorDash

Dynamic Programming Tree Depth-First Search Binary Tree

#50

Rank

#1352HardFrequency: 83%High Priority

Maximum Profit in Job Scheduling

Asked at DoorDash

Array Binary Search Dynamic Programming Sorting

#51

Rank

#560MediumFrequency: 81%High Priority

Subarray Sum Equals K

Array Hash Table Prefix Sum

#52

Rank

#1894EasyFrequency: 80%High Priority

Merge Strings Alternately

Asked at Google

Two Pointers String

#53

Rank

#14EasyFrequency: 80%High Priority

Longest Common Prefix

#54

Rank

#53MediumFrequency: 79%High Priority

Maximum Subarray

Asked at Microsoft

Array Divide and Conquer Dynamic Programming

#55

Rank

#70EasyFrequency: 79%High Priority

Climbing Stairs

Asked at Microsoft

Math Dynamic Programming Memoization

#56

Rank

#1908EasyFrequency: 79%High Priority

Recyclable and Low Fat Products

Asked at Microsoft

#57

Rank

#236MediumFrequency: 79%High Priority

Lowest Common Ancestor of a Binary Tree

Tree Depth-First Search Binary Tree

#58

Rank

#269HardFrequency: 79%High Priority

Alien Dictionary

Array String Depth-First Search Breadth-First Search Graph+1 more

#59

Rank

#305HardFrequency: 79%High Priority

Number of Islands II

Array Hash Table Union Find

#60

Rank

#2809EasyFrequency: 77%High Priority

Create Hello World Function

Asked at Google

#61

Rank

#199MediumFrequency: 76%High Priority

Binary Tree Right Side View

Tree Depth-First Search Breadth-First Search Binary Tree

#62

Rank

#347MediumFrequency: 76%High Priority

Top K Frequent Elements

Array Hash Table Divide and Conquer Sorting Heap (Priority Queue)+3 more

#63

Rank

#1713MediumFrequency: 76%High Priority

Dot Product of Two Sparse Vectors

Array Hash Table Two Pointers Design

#64

Rank

#42HardFrequency: 74%High Priority

Trapping Rain Water

Asked at Amazon

Array Two Pointers Dynamic Programming Stack Monotonic Stack

#65

Rank

#3654MediumFrequency: 74%High Priority

Minimum Array Sum

Asked at Amazon

Array Dynamic Programming

#66

Rank

#543EasyFrequency: 74%High Priority

Diameter of Binary Tree

Tree Depth-First Search Binary Tree

#67

Rank

#27EasyFrequency: 73%High Priority

Remove Element

Asked at Microsoft

Array Two Pointers

#68

Rank

#2383EasyFrequency: 73%High Priority

Add Two Integers

Asked at Microsoft

#69

Rank

#975EasyFrequency: 73%High Priority

Range Sum of BST

Tree Depth-First Search Binary Search Tree Binary Tree

#70

Rank

#224HardFrequency: 73%High Priority

Basic Calculator

Asked at DoorDash

Math String Stack Recursion

#71

Rank

#329HardFrequency: 73%High Priority

Longest Increasing Path in a Matrix

Asked at DoorDash

Array Dynamic Programming Depth-First Search Breadth-First Search Graph+3 more

#72

Rank

#907MediumFrequency: 73%High Priority

Koko Eating Bananas

Asked at DoorDash

Array Binary Search

#73

Rank

#1397MediumFrequency: 73%High Priority

Search Suggestions System

Asked at DoorDash

Array String Binary Search Trie Sorting+1 more

#74

Rank

#1783MediumFrequency: 73%High Priority

Ways to Make a Fair Array

Asked at DoorDash

Array Prefix Sum

#75

Rank

#1915EasyFrequency: 73%High Priority

Check if One String Swap Can Make Strings Equal

Asked at DoorDash

Hash Table String Counting

#76

Rank

#778MediumFrequency: 72%High Priority

Reorganize String

Asked at Amazon

Hash Table String Greedy Sorting Heap (Priority Queue)+1 more

#77

Rank

#3710HardFrequency: 72%High Priority

Design an Array Statistics Tracker

Asked at Amazon

Hash Table Binary Search Design Queue Heap (Priority Queue)+2 more

#78

Rank

#23HardFrequency: 72%High Priority

Merge k Sorted Lists

Linked List Divide and Conquer Heap (Priority Queue)Merge Sort

#79

Rank

#56MediumFrequency: 72%High Priority

Merge Intervals

#80

Rank

#39MediumFrequency: 72%High Priority

Combination Sum

Asked at TikTok

Array Backtracking

#81

Rank

#139MediumFrequency: 72%High Priority

Word Break

Asked at TikTok

Array Hash Table String Dynamic Programming Trie+1 more

#82

Rank

#1929MediumFrequency: 72%High Priority

Maximum Value at a Given Index in a Bounded Array

Asked at TikTok

Binary Search Greedy

#83

Rank

#235MediumFrequency: 72%High Priority

Lowest Common Ancestor of a Binary Search Tree

Asked at LinkedIn

Tree Depth-First Search Binary Search Tree Binary Tree

#84

Rank

#277MediumFrequency: 72%High Priority

Find the Celebrity

Asked at LinkedIn

Two Pointers Graph Interactive

#85

Rank

#381HardFrequency: 72%High Priority

Insert Delete GetRandom O(1) - Duplicates allowed

Asked at LinkedIn

Array Hash Table Math Design Randomized

#86

Rank

#605EasyFrequency: 72%High Priority

Can Place Flowers

Asked at LinkedIn

#87

Rank

#2MediumFrequency: 71%High Priority

Add Two Numbers

Asked at Google

Linked List Math Recursion

#88

Rank

#20EasyFrequency: 71%High Priority

Valid Parentheses

#89

Rank

#127HardFrequency: 71%High Priority

Word Ladder

Hash Table String Breadth-First Search

#90

Rank

#121EasyFrequency: 69%High Priority

Best Time to Buy and Sell Stock

Asked at Amazon

Array Dynamic Programming

#91

Rank

#1108MediumFrequency: 69%High Priority

Analyze User Website Visit Pattern

Asked at Amazon

Array Hash Table Sorting

#92

Rank

#65HardFrequency: 69%High Priority

Valid Number

#93

Rank

#1028MediumFrequency: 69%High Priority

Interval List Intersections

Array Two Pointers

#94

Rank

#129MediumFrequency: 68%High Priority

Sum Root to Leaf Numbers

Tree Depth-First Search Binary Tree

#95

Rank

#1014MediumFrequency: 68%High Priority

K Closest Points to Origin

Array Math Divide and Conquer Geometry Sorting+2 more

#96

Rank

#4HardFrequency: 67%High Priority

Median of Two Sorted Arrays

Asked at Google

Array Binary Search Divide and Conquer

#97

Rank

#1085MediumFrequency: 67%High Priority

The Earliest Moment When Everyone Become Friends

Asked at Google

Array Union Find Sorting

#98

Rank

#3639MediumFrequency: 67%High Priority

Zero Array Transformation I

Asked at Google

Array Prefix Sum

#99

Rank

#3647MediumFrequency: 67%High Priority

Zero Array Transformation III

Asked at Google

Array Greedy Sorting Heap (Priority Queue)Prefix Sum

#100

Rank

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