System Design Interview Prep

Rank

#3594MediumFrequency: 100%High Priority

Identify the Largest Outlier in an Array

Array Hash Table Counting Enumeration

Rank

#3655MediumFrequency: 100%High Priority

Digit Operations to Make Two Integers Equal

Math Graph Heap (Priority Queue)Number Theory Shortest Path

Rank

#232EasyFrequency: 100%High Priority

Implement Queue using Stacks

Stack Design Queue

Rank

#3613MediumFrequency: 100%High Priority

Maximize Amount After Two Days of Conversions

Array String Depth-First Search Breadth-First Search Graph

Rank

#716HardFrequency: 100%High Priority

Max Stack

Linked List Stack Design Doubly-Linked List Ordered Set

Rank

#817EasyFrequency: 100%High Priority

Design HashMap

Asked at DoorDash

Array Hash Table Linked List Design Hash Function

Rank

#694MediumFrequency: 98%High Priority

Number of Distinct Islands

Hash Table Depth-First Search Breadth-First Search Union Find Hash Function

Rank

#314MediumFrequency: 97%High Priority

Binary Tree Vertical Order Traversal

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

Rank

#833HardFrequency: 95%High Priority

Bus Routes

Array Hash Table Breadth-First Search

#10

Rank

#215MediumFrequency: 92%High Priority

Kth Largest Element in an Array

Array Divide and Conquer Sorting Heap (Priority Queue)Quickselect

#11

Rank

#1790MediumFrequency: 91%High Priority

Lowest Common Ancestor of a Binary Tree III

Hash Table Two Pointers Tree Binary Tree

#12

Rank

#129MediumFrequency: 91%High Priority

Sum Root to Leaf Numbers

#13

Rank

#1423MediumFrequency: 91%High Priority

Maximum Number of Occurrences of a Substring

#14

Rank

#146MediumFrequency: 88%High Priority

LRU Cache

#15

Rank

#998MediumFrequency: 87%High Priority

Check Completeness of a Binary Tree

Tree Breadth-First Search Binary Tree

#16

Rank

#621MediumFrequency: 85%High Priority

Task Scheduler

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

#17

Rank

#3MediumFrequency: 84%High Priority

Longest Substring Without Repeating Characters

#18

Rank

#366MediumFrequency: 84%High Priority

Find Leaves of Binary Tree

#19

Rank

#124HardFrequency: 84%High Priority

Binary Tree Maximum Path Sum

Dynamic Programming Tree Depth-First Search Binary Tree

#20

Rank

#387EasyFrequency: 83%High Priority

First Unique Character in a String

Hash Table String Queue Counting

#21

Rank

#1330MediumFrequency: 83%High Priority

Longest Arithmetic Subsequence of Given Difference

Asked at Airbnb

Array Hash Table Dynamic Programming

#22

Rank

#1108MediumFrequency: 83%High Priority

Analyze User Website Visit Pattern

Array Hash Table Sorting

#23

Rank

#772MediumFrequency: 83%High Priority

Construct Quad Tree

Array Divide and Conquer Tree Matrix

#24

Rank

#424MediumFrequency: 82%High Priority

Longest Repeating Character Replacement

#25

Rank

#398MediumFrequency: 82%High Priority

Random Pick Index

Hash Table Math Reservoir Sampling Randomized

#26

Rank

#1014MediumFrequency: 82%High Priority

K Closest Points to Origin

Array Math Divide and Conquer Geometry Sorting+2 more

#27

Rank

#141EasyFrequency: 82%High Priority

Linked List Cycle

Hash Table Linked List Two Pointers

#28

Rank

#432HardFrequency: 82%High Priority

All O`one Data Structure

#29

Rank

#560MediumFrequency: 81%High Priority

Subarray Sum Equals K

Array Hash Table Prefix Sum

#30

Rank

#348MediumFrequency: 81%High Priority

Design Tic-Tac-Toe

Array Hash Table Design Matrix Simulation

#31

Rank

#104EasyFrequency: 80%High Priority

Maximum Depth of Binary Tree

Tree Depth-First Search Breadth-First Search Binary Tree

#32

Rank

#236MediumFrequency: 79%High Priority

Lowest Common Ancestor of a Binary Tree

#33

Rank

#269HardFrequency: 79%High Priority

Alien Dictionary

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

#34

Rank

#305HardFrequency: 79%High Priority

Number of Islands II

Array Hash Table Union Find

#35

Rank

#362MediumFrequency: 79%High Priority

Design Hit Counter

Array Binary Search Design Queue Data Stream

#36

Rank

#380MediumFrequency: 79%High Priority

Insert Delete GetRandom O(1)

Array Hash Table Math Design Randomized

#37

Rank

#109MediumFrequency: 79%High Priority

Convert Sorted List to Binary Search Tree

Linked List Divide and Conquer Tree Binary Search Tree Binary Tree

#38

Rank

#329HardFrequency: 79%High Priority

Longest Increasing Path in a Matrix

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

#39

Rank

#166MediumFrequency: 79%High Priority

Fraction to Recurring Decimal

Hash Table Math String

#40

Rank

#356MediumFrequency: 77%High Priority

Line Reflection

Array Hash Table Math

#41

Rank

#199MediumFrequency: 76%High Priority

Binary Tree Right Side View

Tree Depth-First Search Breadth-First Search Binary Tree

#42

Rank

#347MediumFrequency: 76%High Priority

Top K Frequent Elements

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

#43

Rank

#1713MediumFrequency: 76%High Priority

Dot Product of Two Sparse Vectors

Array Hash Table Two Pointers Design

#44

Rank

#2267HardFrequency: 76%High Priority

Minimum Difference in Sums After Removal of Elements

Array Dynamic Programming Heap (Priority Queue)

#45

Rank

#1478MediumFrequency: 76%High Priority

Maximum Number of Events That Can Be Attended

Array Greedy Sorting Heap (Priority Queue)

#46

Rank

#249MediumFrequency: 76%High Priority

Group Shifted Strings

Array Hash Table String

#47

Rank

#3555EasyFrequency: 76%High Priority

Final Array State After K Multiplication Operations I

Array Math Heap (Priority Queue)Simulation

#48

Rank

#173MediumFrequency: 75%High Priority

Binary Search Tree Iterator

Stack Tree Design Binary Search Tree Binary Tree+1 more

#49

Rank

#543EasyFrequency: 74%High Priority

Diameter of Binary Tree

#50

Rank

#41HardFrequency: 74%High Priority

First Missing Positive

#51

Rank

#346EasyFrequency: 74%High Priority

Moving Average from Data Stream

Array Design Queue Data Stream

#52

Rank

#975EasyFrequency: 73%High Priority

Range Sum of BST

Tree Depth-First Search Binary Search Tree Binary Tree

#53

Rank

#2711HardFrequency: 73%High Priority

Minimum Time to Visit a Cell In a Grid

Array Breadth-First Search Graph Heap (Priority Queue)Matrix+1 more

#54

Rank

#49MediumFrequency: 72%High Priority

Group Anagrams

Array Hash Table String Sorting

#55

Rank

#778MediumFrequency: 72%High Priority

Reorganize String

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

#56

Rank

#3710HardFrequency: 72%High Priority

Design an Array Statistics Tracker

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

#57

Rank

#23HardFrequency: 72%High Priority

Merge k Sorted Lists

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

#58

Rank

#235MediumFrequency: 72%High Priority

Lowest Common Ancestor of a Binary Search Tree

Tree Depth-First Search Binary Search Tree Binary Tree

#59

Rank

#277MediumFrequency: 72%High Priority

Find the Celebrity

Two Pointers Graph Interactive

#60

Rank

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Beginner-Friendly Interview Questions

Easy to medium difficulty problems perfect for interview preparation beginners.

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Advanced Interview Problems

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Hash Table (31)Array (29)Tree (15)Depth-First Search (14)Binary Tree (14)Heap (Priority Queue) (12)Design (12)String (10)

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System Design Interview Prep

Coding problems that help build system design thinking and scalability concepts.

Total Problems

Easy

Medium

Hard

83%

Avg Frequency

Most Common Topics

Companies Asking These Questions

Meta (11)Flipkart (6)Amazon (5)Uber (5)Infosys (5)LinkedIn (4)

Problems in This Collection

#1EasyFrequency: 100%High Priority

Two Sum

Asked at Google

Rank

#3594MediumFrequency: 100%High Priority

Identify the Largest Outlier in an Array

Array Hash Table Counting Enumeration

Rank

#3655MediumFrequency: 100%High Priority

Digit Operations to Make Two Integers Equal

Math Graph Heap (Priority Queue)Number Theory Shortest Path

Rank

#232EasyFrequency: 100%High Priority

Implement Queue using Stacks

Stack Design Queue

Rank

#3613MediumFrequency: 100%High Priority

Maximize Amount After Two Days of Conversions

Array String Depth-First Search Breadth-First Search Graph

Rank

#716HardFrequency: 100%High Priority

Max Stack

Linked List Stack Design Doubly-Linked List Ordered Set

Rank

#817EasyFrequency: 100%High Priority

Design HashMap

Asked at DoorDash

Array Hash Table Linked List Design Hash Function

Rank

#694MediumFrequency: 98%High Priority

Number of Distinct Islands

Hash Table Depth-First Search Breadth-First Search Union Find Hash Function

Rank

#314MediumFrequency: 97%High Priority

Binary Tree Vertical Order Traversal

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

Rank

#833HardFrequency: 95%High Priority

Bus Routes

Array Hash Table Breadth-First Search

#10

Rank

#215MediumFrequency: 92%High Priority

Kth Largest Element in an Array

Array Divide and Conquer Sorting Heap (Priority Queue)Quickselect

#11

Rank

#1790MediumFrequency: 91%High Priority

Lowest Common Ancestor of a Binary Tree III

Hash Table Two Pointers Tree Binary Tree

#12

Rank

#129MediumFrequency: 91%High Priority

Sum Root to Leaf Numbers

#13

Rank

#1423MediumFrequency: 91%High Priority

Maximum Number of Occurrences of a Substring

#14

Rank

#146MediumFrequency: 88%High Priority

LRU Cache

#15

Rank

#998MediumFrequency: 87%High Priority

Check Completeness of a Binary Tree

Tree Breadth-First Search Binary Tree

#16

Rank

#621MediumFrequency: 85%High Priority

Task Scheduler

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

#17

Rank

#3MediumFrequency: 84%High Priority

Longest Substring Without Repeating Characters

#18

Rank

#366MediumFrequency: 84%High Priority

Find Leaves of Binary Tree

#19

Rank

#124HardFrequency: 84%High Priority

Binary Tree Maximum Path Sum

Dynamic Programming Tree Depth-First Search Binary Tree

#20

Rank

#387EasyFrequency: 83%High Priority

First Unique Character in a String

Hash Table String Queue Counting

#21

Rank

#1330MediumFrequency: 83%High Priority

Longest Arithmetic Subsequence of Given Difference

Asked at Airbnb

Array Hash Table Dynamic Programming

#22

Rank

#1108MediumFrequency: 83%High Priority

Analyze User Website Visit Pattern

Array Hash Table Sorting

#23

Rank

#772MediumFrequency: 83%High Priority

Construct Quad Tree

Array Divide and Conquer Tree Matrix

#24

Rank

#424MediumFrequency: 82%High Priority

Longest Repeating Character Replacement

#25

Rank

#398MediumFrequency: 82%High Priority

Random Pick Index

Hash Table Math Reservoir Sampling Randomized

#26

Rank

#1014MediumFrequency: 82%High Priority

K Closest Points to Origin

Array Math Divide and Conquer Geometry Sorting+2 more

#27

Rank

#141EasyFrequency: 82%High Priority

Linked List Cycle

Hash Table Linked List Two Pointers

#28

Rank

#432HardFrequency: 82%High Priority

All O`one Data Structure

#29

Rank

#560MediumFrequency: 81%High Priority

Subarray Sum Equals K

Array Hash Table Prefix Sum

#30

Rank

#348MediumFrequency: 81%High Priority

Design Tic-Tac-Toe

Array Hash Table Design Matrix Simulation

#31

Rank

#104EasyFrequency: 80%High Priority

Maximum Depth of Binary Tree

Tree Depth-First Search Breadth-First Search Binary Tree

#32

Rank

#236MediumFrequency: 79%High Priority

Lowest Common Ancestor of a Binary Tree

#33

Rank

#269HardFrequency: 79%High Priority

Alien Dictionary

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

#34

Rank

#305HardFrequency: 79%High Priority

Number of Islands II

Array Hash Table Union Find

#35

Rank

#362MediumFrequency: 79%High Priority

Design Hit Counter

Array Binary Search Design Queue Data Stream

#36

Rank

#380MediumFrequency: 79%High Priority

Insert Delete GetRandom O(1)

Array Hash Table Math Design Randomized

#37

Rank

#109MediumFrequency: 79%High Priority

Convert Sorted List to Binary Search Tree

Linked List Divide and Conquer Tree Binary Search Tree Binary Tree

#38

Rank

#329HardFrequency: 79%High Priority

Longest Increasing Path in a Matrix

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

#39

Rank

#166MediumFrequency: 79%High Priority

Fraction to Recurring Decimal

Hash Table Math String

#40

Rank

#356MediumFrequency: 77%High Priority

Line Reflection

Array Hash Table Math

#41

Rank

#199MediumFrequency: 76%High Priority

Binary Tree Right Side View

Tree Depth-First Search Breadth-First Search Binary Tree

#42

Rank

#347MediumFrequency: 76%High Priority

Top K Frequent Elements

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

#43

Rank

#1713MediumFrequency: 76%High Priority

Dot Product of Two Sparse Vectors

Array Hash Table Two Pointers Design

#44

Rank

#2267HardFrequency: 76%High Priority

Minimum Difference in Sums After Removal of Elements

Array Dynamic Programming Heap (Priority Queue)

#45

Rank

#1478MediumFrequency: 76%High Priority

Maximum Number of Events That Can Be Attended

Array Greedy Sorting Heap (Priority Queue)

#46

Rank

#249MediumFrequency: 76%High Priority

Group Shifted Strings

Array Hash Table String

#47

Rank

#3555EasyFrequency: 76%High Priority

Final Array State After K Multiplication Operations I

Array Math Heap (Priority Queue)Simulation

#48

Rank

#173MediumFrequency: 75%High Priority

Binary Search Tree Iterator

Stack Tree Design Binary Search Tree Binary Tree+1 more

#49

Rank

#543EasyFrequency: 74%High Priority

Diameter of Binary Tree

#50

Rank

#41HardFrequency: 74%High Priority

First Missing Positive

#51

Rank

#346EasyFrequency: 74%High Priority

Moving Average from Data Stream

Array Design Queue Data Stream

#52

Rank

#975EasyFrequency: 73%High Priority

Range Sum of BST

Tree Depth-First Search Binary Search Tree Binary Tree

#53

Rank

#2711HardFrequency: 73%High Priority

Minimum Time to Visit a Cell In a Grid

Array Breadth-First Search Graph Heap (Priority Queue)Matrix+1 more

#54

Rank

#49MediumFrequency: 72%High Priority

Group Anagrams

Array Hash Table String Sorting

#55

Rank

#778MediumFrequency: 72%High Priority

Reorganize String

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

#56

Rank

#3710HardFrequency: 72%High Priority

Design an Array Statistics Tracker

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

#57

Rank

#23HardFrequency: 72%High Priority

Merge k Sorted Lists

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

#58

Rank

#235MediumFrequency: 72%High Priority

Lowest Common Ancestor of a Binary Search Tree

Tree Depth-First Search Binary Search Tree Binary Tree

#59

Rank

#277MediumFrequency: 72%High Priority

Find the Celebrity

Two Pointers Graph Interactive

#60

Rank

Other Collections

Most Frequent Interview Questions

The top 50 most frequently asked coding interview questions across all major tech companies.

Beginner-Friendly Interview Questions

Easy to medium difficulty problems perfect for interview preparation beginners.

75 problems →

Advanced Interview Problems

Challenging hard problems asked at top-tier tech companies for senior positions.