Hard LeetCode Interview Questions

Master 40 hard difficulty coding problems frequently asked in technical interviews at top tech companies. Perfect for building confidence and fundamental problem-solving skills.

Easy (110)Medium (260)Hard (67)

#3638HardFrequency: 100%

Minimum Operations to Make Character Frequencies Equal

Asked at TikTok

Hash Table String Dynamic Programming Counting Enumeration

Rank

#716HardFrequency: 100%

Max Stack

Asked at LinkedIn

Linked List Stack Design Doubly-Linked List Ordered Set

Rank

#295HardFrequency: 100%

Find Median from Data Stream

Asked at PayPal

Two Pointers Design Sorting Heap (Priority Queue)Data Stream

Rank

#833HardFrequency: 95%

Bus Routes

Asked at Uber

Array Hash Table Breadth-First Search

Rank

#460HardFrequency: 88%

LFU Cache

Asked at Salesforce

Hash Table Linked List Design Doubly-Linked List

Rank

#124HardFrequency: 83%

Binary Tree Maximum Path Sum

Asked at DoorDash

Dynamic Programming Tree Depth-First Search Binary Tree

Rank

#1352HardFrequency: 83%

Maximum Profit in Job Scheduling

Asked at DoorDash

Array Binary Search Dynamic Programming Sorting

Rank

#269HardFrequency: 79%

Alien Dictionary

Asked at Uber

Array String Depth-First Search Breadth-First Search Graph Topological Sort

Rank

#305HardFrequency: 79%

Number of Islands II

Asked at Uber

Array Hash Table Union Find

Rank

#42HardFrequency: 74%

Trapping Rain Water

Asked at Amazon

Array Two Pointers Dynamic Programming Stack Monotonic Stack

#10

Rank

#224HardFrequency: 73%

Basic Calculator

Asked at DoorDash

Math String Stack Recursion

#11

Rank

#329HardFrequency: 73%

Longest Increasing Path in a Matrix

Asked at DoorDash

Array Dynamic Programming Depth-First Search Breadth-First Search Graph Topological Sort Memoization Matrix

#12

Rank

#3710HardFrequency: 72%

Design an Array Statistics Tracker

Asked at Amazon

Hash Table Binary Search Design Queue Heap (Priority Queue)Data Stream Ordered Set

#13

Rank

#23HardFrequency: 72%

Merge k Sorted Lists

Asked at Meta

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

#14

Rank

#381HardFrequency: 72%

Insert Delete GetRandom O(1) - Duplicates allowed

Asked at LinkedIn

Array Hash Table Math Design Randomized

#15

Rank

#127HardFrequency: 71%

Word Ladder

Asked at Apple

Hash Table String Breadth-First Search

#16

Rank

#65HardFrequency: 69%

Valid Number

Asked at Meta

String

#17

Rank

#4HardFrequency: 67%

Median of Two Sorted Arrays

Asked at Google

Array Binary Search Divide and Conquer

#18

Rank

#2267HardFrequency: 64%

Minimum Difference in Sums After Removal of Elements

Asked at Amazon

Array Dynamic Programming Heap (Priority Queue)

#19

Rank

#432HardFrequency: 63%

All O`one Data Structure

Asked at LinkedIn

Hash Table Linked List Design Doubly-Linked List

#20

Rank

#1178HardFrequency: 62%

Valid Palindrome III

Asked at Meta

String Dynamic Programming

#21

Rank

#76HardFrequency: 60%

Minimum Window Substring

Asked at Meta

Hash Table String Sliding Window

#22

Rank

#854HardFrequency: 60%

Making A Large Island

Asked at Meta

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

#23

Rank

#1029HardFrequency: 60%

Vertical Order Traversal of a Binary Tree

Asked at Meta

Hash Table Tree Depth-First Search Breadth-First Search Sorting Binary Tree

#24

Rank

#273HardFrequency: 55%

Integer to English Words

Asked at Microsoft

Math String Recursion

#25

Rank

#629HardFrequency: 55%

K Inverse Pairs Array

Asked at Microsoft

Dynamic Programming

#26

Rank

#2711HardFrequency: 55%

Minimum Time to Visit a Cell In a Grid

Asked at Microsoft

Array Breadth-First Search Graph Heap (Priority Queue)Matrix Shortest Path

#27

Rank

#51HardFrequency: 48%

N-Queens

Asked at Google

Array Backtracking

#28

Rank

#10HardFrequency: 45%

Regular Expression Matching

Asked at Amazon

String Dynamic Programming Recursion

#29

Rank

#84HardFrequency: 45%

Largest Rectangle in Histogram

Asked at Amazon

Array Stack Monotonic Stack

#30

Rank

#126HardFrequency: 45%

Word Ladder II

Asked at Amazon

Hash Table String Backtracking Breadth-First Search

#31

Rank

#239HardFrequency: 45%

Sliding Window Maximum

Asked at Amazon

Array Queue Sliding Window Heap (Priority Queue)Monotonic Queue

#32

Rank

#262HardFrequency: 45%

Trips and Users

Asked at Amazon

Database

#33

Rank

#1034HardFrequency: 45%

Subarrays with K Different Integers

Asked at Amazon

Array Hash Table Sliding Window Counting

#34

Rank

#3410HardFrequency: 45%

Find Longest Self-Contained Substring

Asked at Amazon

Hash Table String Binary Search Prefix Sum

#35

Rank

#410HardFrequency: 42%

Split Array Largest Sum

Asked at Google

Array Binary Search Dynamic Programming Greedy Prefix Sum

#36

Rank

#282HardFrequency: 37%

Expression Add Operators

Asked at Meta

Math String Backtracking

#37

Rank

#25HardFrequency: 36%

Reverse Nodes in k-Group

Asked at Amazon

Linked List Recursion

#38

Rank

#188HardFrequency: 36%

Best Time to Buy and Sell Stock IV

Asked at Amazon

Array Dynamic Programming

#39

Rank

#41HardFrequency: 33%

First Missing Positive

Asked at Google

Array Hash Table

#40

Rank

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