System Design Interview Prep

Rank

#833HardFrequency: 100%High Priority

Bus Routes

Array Hash Table Breadth-First Search

Rank

#716HardFrequency: 100%High Priority

Max Stack

Linked List Stack Design Doubly-Linked List Ordered Set

Rank

#362MediumFrequency: 100%High Priority

Design Hit Counter

Array Binary Search Design Queue Data Stream

Rank

#1549MediumFrequency: 94.4%High Priority

Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit

Array Queue Sliding Window Heap (Priority Queue)Ordered Set+1 more

Rank

#432HardFrequency: 93.8%High Priority

All O`one Data Structure

Rank

#348MediumFrequency: 93.6%High Priority

Design Tic-Tac-Toe

Array Hash Table Design Matrix Simulation

Rank

#314MediumFrequency: 93.4%High Priority

Binary Tree Vertical Order Traversal

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

Rank

#215MediumFrequency: 93.3%High Priority

Kth Largest Element in an Array

Array Divide and Conquer Sorting Heap (Priority Queue)Quickselect

#10

Rank

#3MediumFrequency: 92.8%High Priority

Longest Substring Without Repeating Characters

Asked at Infosys

#11

Rank

#124HardFrequency: 90.2%High Priority

Binary Tree Maximum Path Sum

Dynamic Programming Tree Depth-First Search Binary Tree DP on Trees

#12

Rank

#305HardFrequency: 89.9%High Priority

Number of Islands II

Array Hash Table Union-Find

#13

Rank

#1790MediumFrequency: 88.5%High Priority

Lowest Common Ancestor of a Binary Tree III

Hash Table Two Pointers Tree Binary Tree Binary Lifting+1 more

#14

Rank

#560MediumFrequency: 87.2%High Priority

Subarray Sum Equals K

Array Hash Table Prefix Sum

#15

Rank

#772MediumFrequency: 87%High Priority

Construct Quad Tree

Array Divide and Conquer Tree Matrix

#16

Rank

#543EasyFrequency: 86.8%High Priority

Diameter of Binary Tree

#17

Rank

#694MediumFrequency: 86.6%High Priority

Number of Distinct Islands

Array Hash Table Depth-First Search Breadth-First Search Union-Find+3 more

#18

Rank

#236MediumFrequency: 86.4%High Priority

Lowest Common Ancestor of a Binary Tree

Tree Depth-First Search Binary Tree Binary Lifting Lowest Common Ancestor

#19

Rank

#251MediumFrequency: 85.6%High Priority

Flatten 2D Vector

Array Two Pointers Design Iterator

#20

Rank

#199MediumFrequency: 85.4%High Priority

Binary Tree Right Side View

Tree Depth-First Search Breadth-First Search Binary Tree

#21

Rank

#438MediumFrequency: 84.4%High Priority

Find All Anagrams in a String

#22

Rank

#253MediumFrequency: 83.8%High Priority

Meeting Rooms II

Array Two Pointers Greedy Sorting Heap (Priority Queue)+1 more

#23

Rank

#2217MediumFrequency: 83.7%High Priority

Step-By-Step Directions From a Binary Tree Node to Another

String Tree Depth-First Search Binary Tree Binary Lifting+1 more

#24

Rank

#1366MediumFrequency: 83.2%High Priority

First Unique Number

Array Hash Table Design Queue Data Stream

#25

Rank

#1112EasyFrequency: 82.7%High Priority

Find Words That Can Be Formed by Characters

Array Hash Table String Counting

#26

Rank

#1397MediumFrequency: 82.5%High Priority

Search Suggestions System

Array String Binary Search Trie Sorting+1 more

#27

Rank

#1190MediumFrequency: 82.4%High Priority

Smallest Common Region

Array Hash Table String Tree Depth-First Search+3 more

#28

Rank

#230MediumFrequency: 82.3%High Priority

Kth Smallest Element in a BST

Tree Depth-First Search Binary Search Tree Binary Tree

#29

Rank

#244MediumFrequency: 82.3%High Priority

Shortest Word Distance II

Array Hash Table Two Pointers String Design

#30

Rank

#49MediumFrequency: 81.6%High Priority

Group Anagrams

Array Hash Table String Sorting

#31

Rank

#347MediumFrequency: 81.3%High Priority

Top K Frequent Elements

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

#32

Rank

#1023MediumFrequency: 79.9%High Priority

Time Based Key-Value Store

Hash Table String Binary Search Design

#33

Rank

#1713MediumFrequency: 79.6%High Priority

Dot Product of Two Sparse Vectors

Array Hash Table Two Pointers Design Linear Algebra

#34

Rank

#2023HardFrequency: 79.4%High Priority

Design Movie Rental System

Array Hash Table Design Heap (Priority Queue)Ordered Set

#35

Rank

#127HardFrequency: 79%High Priority

Word Ladder

Hash Table String Breadth-First Search Bidirectional Search

#36

Rank

#460HardFrequency: 78.9%High Priority

LFU Cache

#37

Rank

#336HardFrequency: 78.6%High Priority

Palindrome Pairs

Array Hash Table String Trie Hash Function

#38

Rank

#631HardFrequency: 78.6%High Priority

Design Excel Sum Formula

Array Hash Table String Graph Theory Design+2 more

#39

Rank

#129MediumFrequency: 78.4%High Priority

Sum Root to Leaf Numbers

Tree Depth-First Search Binary Tree

#40

Rank

#4180MediumFrequency: 78.4%High Priority

Pythagorean Distance Nodes in a Tree

Tree Breadth-First Search

#41

Rank

#778MediumFrequency: 78.3%High Priority

Reorganize String

Asked at Amazon

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

#42

Rank

#138MediumFrequency: 78.1%High Priority

Copy List with Random Pointer

Hash Table Linked List

#43

Rank

#975EasyFrequency: 78%High Priority

Range Sum of BST

Tree Depth-First Search Binary Search Tree Binary Tree

#44

Rank

#1014MediumFrequency: 77.1%High Priority

K Closest Points to Origin

Array Math Divide and Conquer Geometry Sorting+3 more

#45

Rank

#366MediumFrequency: 76.7%High Priority

Find Leaves of Binary Tree

#46

Rank

#2147HardFrequency: 76.6%High Priority

The Score of Students Solving Math Expression

Array Hash Table Math String Dynamic Programming+2 more

#47

Rank

#2230MediumFrequency: 76.6%High Priority

Minimum Cost to Reach City With Discounts

Graph Theory Heap (Priority Queue)Shortest Path Dijkstra's Algorithm

#48

Rank

#1024HardFrequency: 76.6%High Priority

Triples with Bitwise AND Equal To Zero

Array Hash Table Bit Manipulation

#49

Rank

#3994EasyFrequency: 76.6%High Priority

Find The Least Frequent Digit

Array Hash Table Math Counting

#50

Rank

#380MediumFrequency: 76.2%High Priority

Insert Delete GetRandom O(1)

Array Hash Table Math Design Randomized

#51

Rank

#2640MediumFrequency: 76%High Priority

Maximum Number of Integers to Choose From a Range I

Array Hash Table Binary Search Greedy Sorting

#52

Rank

#2667HardFrequency: 76%High Priority

Maximum Frequency Score of a Subarray

Array Hash Table Math Stack Sliding Window

#53

Rank

#36MediumFrequency: 75.8%High Priority

Valid Sudoku

Array Hash Table Matrix

#54

Rank

#3750MediumFrequency: 75.5%High Priority

Closest Equal Element Queries

Array Hash Table Binary Search

#55

Rank

#23HardFrequency: 75.1%High Priority

Merge k Sorted Lists

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

#56

Rank

#76HardFrequency: 74.7%High Priority

Minimum Window Substring

#57

Rank

#1962MediumFrequency: 74.6%High Priority

Single-Threaded CPU

Array Sorting Heap (Priority Queue)

#58

Rank

#239HardFrequency: 74.4%High Priority

Sliding Window Maximum

Array Queue Sliding Window Heap (Priority Queue)Monotonic Queue+1 more

#59

Rank

#160EasyFrequency: 73.9%High Priority

Intersection of Two Linked Lists

Hash Table Linked List Two Pointers

#60

Rank

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Hash Table (37)Array (34)String (15)Design (14)Tree (14)Heap (Priority Queue) (12)Depth-First Search (12)Sorting (11)

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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 (14)Uber (7)LinkedIn (5)Databricks (5)Airbnb (5)Flipkart (5)

Problems in This Collection

#1EasyFrequency: 100%High Priority

Two Sum

Asked at Google

Array Hash Table

Rank

#146MediumFrequency: 100%High Priority

LRU Cache

Rank

#833HardFrequency: 100%High Priority

Bus Routes

Array Hash Table Breadth-First Search

Rank

#716HardFrequency: 100%High Priority

Max Stack

Linked List Stack Design Doubly-Linked List Ordered Set

Rank

#362MediumFrequency: 100%High Priority

Design Hit Counter

Array Binary Search Design Queue Data Stream

Rank

#1549MediumFrequency: 94.4%High Priority

Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit

Array Queue Sliding Window Heap (Priority Queue)Ordered Set+1 more

Rank

#432HardFrequency: 93.8%High Priority

All O`one Data Structure

Rank

#348MediumFrequency: 93.6%High Priority

Design Tic-Tac-Toe

Array Hash Table Design Matrix Simulation

Rank

#314MediumFrequency: 93.4%High Priority

Binary Tree Vertical Order Traversal

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

Rank

#215MediumFrequency: 93.3%High Priority

Kth Largest Element in an Array

Array Divide and Conquer Sorting Heap (Priority Queue)Quickselect

#10

Rank

#3MediumFrequency: 92.8%High Priority

Longest Substring Without Repeating Characters

Asked at Infosys

#11

Rank

#124HardFrequency: 90.2%High Priority

Binary Tree Maximum Path Sum

Dynamic Programming Tree Depth-First Search Binary Tree DP on Trees

#12

Rank

#305HardFrequency: 89.9%High Priority

Number of Islands II

Array Hash Table Union-Find

#13

Rank

#1790MediumFrequency: 88.5%High Priority

Lowest Common Ancestor of a Binary Tree III

Hash Table Two Pointers Tree Binary Tree Binary Lifting+1 more

#14

Rank

#560MediumFrequency: 87.2%High Priority

Subarray Sum Equals K

Array Hash Table Prefix Sum

#15

Rank

#772MediumFrequency: 87%High Priority

Construct Quad Tree

Array Divide and Conquer Tree Matrix

#16

Rank

#543EasyFrequency: 86.8%High Priority

Diameter of Binary Tree

#17

Rank

#694MediumFrequency: 86.6%High Priority

Number of Distinct Islands

Array Hash Table Depth-First Search Breadth-First Search Union-Find+3 more

#18

Rank

#236MediumFrequency: 86.4%High Priority

Lowest Common Ancestor of a Binary Tree

Tree Depth-First Search Binary Tree Binary Lifting Lowest Common Ancestor

#19

Rank

#251MediumFrequency: 85.6%High Priority

Flatten 2D Vector

Array Two Pointers Design Iterator

#20

Rank

#199MediumFrequency: 85.4%High Priority

Binary Tree Right Side View

Tree Depth-First Search Breadth-First Search Binary Tree

#21

Rank

#438MediumFrequency: 84.4%High Priority

Find All Anagrams in a String

#22

Rank

#253MediumFrequency: 83.8%High Priority

Meeting Rooms II

Array Two Pointers Greedy Sorting Heap (Priority Queue)+1 more

#23

Rank

#2217MediumFrequency: 83.7%High Priority

Step-By-Step Directions From a Binary Tree Node to Another

String Tree Depth-First Search Binary Tree Binary Lifting+1 more

#24

Rank

#1366MediumFrequency: 83.2%High Priority

First Unique Number

Array Hash Table Design Queue Data Stream

#25

Rank

#1112EasyFrequency: 82.7%High Priority

Find Words That Can Be Formed by Characters

Array Hash Table String Counting

#26

Rank

#1397MediumFrequency: 82.5%High Priority

Search Suggestions System

Array String Binary Search Trie Sorting+1 more

#27

Rank

#1190MediumFrequency: 82.4%High Priority

Smallest Common Region

Array Hash Table String Tree Depth-First Search+3 more

#28

Rank

#230MediumFrequency: 82.3%High Priority

Kth Smallest Element in a BST

Tree Depth-First Search Binary Search Tree Binary Tree

#29

Rank

#244MediumFrequency: 82.3%High Priority

Shortest Word Distance II

Array Hash Table Two Pointers String Design

#30

Rank

#49MediumFrequency: 81.6%High Priority

Group Anagrams

Array Hash Table String Sorting

#31

Rank

#347MediumFrequency: 81.3%High Priority

Top K Frequent Elements

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

#32

Rank

#1023MediumFrequency: 79.9%High Priority

Time Based Key-Value Store

Hash Table String Binary Search Design

#33

Rank

#1713MediumFrequency: 79.6%High Priority

Dot Product of Two Sparse Vectors

Array Hash Table Two Pointers Design Linear Algebra

#34

Rank

#2023HardFrequency: 79.4%High Priority

Design Movie Rental System

Array Hash Table Design Heap (Priority Queue)Ordered Set

#35

Rank

#127HardFrequency: 79%High Priority

Word Ladder

Hash Table String Breadth-First Search Bidirectional Search

#36

Rank

#460HardFrequency: 78.9%High Priority

LFU Cache

#37

Rank

#336HardFrequency: 78.6%High Priority

Palindrome Pairs

Array Hash Table String Trie Hash Function

#38

Rank

#631HardFrequency: 78.6%High Priority

Design Excel Sum Formula

Array Hash Table String Graph Theory Design+2 more

#39

Rank

#129MediumFrequency: 78.4%High Priority

Sum Root to Leaf Numbers

Tree Depth-First Search Binary Tree

#40

Rank

#4180MediumFrequency: 78.4%High Priority

Pythagorean Distance Nodes in a Tree

Tree Breadth-First Search

#41

Rank

#778MediumFrequency: 78.3%High Priority

Reorganize String

Asked at Amazon

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

#42

Rank

#138MediumFrequency: 78.1%High Priority

Copy List with Random Pointer

Hash Table Linked List

#43

Rank

#975EasyFrequency: 78%High Priority

Range Sum of BST

Tree Depth-First Search Binary Search Tree Binary Tree

#44

Rank

#1014MediumFrequency: 77.1%High Priority

K Closest Points to Origin

Array Math Divide and Conquer Geometry Sorting+3 more

#45

Rank

#366MediumFrequency: 76.7%High Priority

Find Leaves of Binary Tree

#46

Rank

#2147HardFrequency: 76.6%High Priority

The Score of Students Solving Math Expression

Array Hash Table Math String Dynamic Programming+2 more

#47

Rank

#2230MediumFrequency: 76.6%High Priority

Minimum Cost to Reach City With Discounts

Graph Theory Heap (Priority Queue)Shortest Path Dijkstra's Algorithm

#48

Rank

#1024HardFrequency: 76.6%High Priority

Triples with Bitwise AND Equal To Zero

Array Hash Table Bit Manipulation

#49

Rank

#3994EasyFrequency: 76.6%High Priority

Find The Least Frequent Digit

Array Hash Table Math Counting

#50

Rank

#380MediumFrequency: 76.2%High Priority

Insert Delete GetRandom O(1)

Array Hash Table Math Design Randomized

#51

Rank

#2640MediumFrequency: 76%High Priority

Maximum Number of Integers to Choose From a Range I

Array Hash Table Binary Search Greedy Sorting

#52

Rank

#2667HardFrequency: 76%High Priority

Maximum Frequency Score of a Subarray

Array Hash Table Math Stack Sliding Window

#53

Rank

#36MediumFrequency: 75.8%High Priority

Valid Sudoku

Array Hash Table Matrix

#54

Rank

#3750MediumFrequency: 75.5%High Priority

Closest Equal Element Queries

Array Hash Table Binary Search

#55

Rank

#23HardFrequency: 75.1%High Priority

Merge k Sorted Lists

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

#56

Rank

#76HardFrequency: 74.7%High Priority

Minimum Window Substring

#57

Rank

#1962MediumFrequency: 74.6%High Priority

Single-Threaded CPU

Array Sorting Heap (Priority Queue)

#58

Rank

#239HardFrequency: 74.4%High Priority

Sliding Window Maximum

Array Queue Sliding Window Heap (Priority Queue)Monotonic Queue+1 more

#59

Rank

#160EasyFrequency: 73.9%High Priority

Intersection of Two Linked Lists

Hash Table Linked List Two Pointers

#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.