Stack Interview Questions

Rank

#716HardFrequency: 100%

Max Stack

Linked List Stack Design Doubly-Linked List Ordered Set

Rank

#364MediumFrequency: 95.4%

Nested List Weight Sum II

Stack Depth-First Search Breadth-First Search

Rank

#227MediumFrequency: 89.3%

Basic Calculator II

Math String Stack

Rank

#42HardFrequency: 88%

Trapping Rain Water

Array Two Pointers Dynamic Programming Stack Monotonic Stack

Rank

#71MediumFrequency: 83.7%

Simplify Path

Rank

#1909MediumFrequency: 82.6%

Buildings With an Ocean View

Rank

#20EasyFrequency: 79%

Valid Parentheses

Rank

#2147HardFrequency: 76.6%

The Score of Students Solving Math Expression

Array Hash Table Math String Dynamic Programming Stack Memoization

Rank

#2667HardFrequency: 76%

Maximum Frequency Score of a Subarray

Array Hash Table Math Stack Sliding Window

#10

Rank

#394MediumFrequency: 75.8%

Decode String

#11

Rank

#957MediumFrequency: 71.8%

Minimum Add to Make Parentheses Valid

#12

Rank

#2419HardFrequency: 69.8%

Subarray With Elements Greater Than Varying Threshold

Array Stack Union-Find Monotonic Stack

#13

Rank

#3181HardFrequency: 69.8%

Find Building Where Alice and Bob Can Meet

Array Binary Search Stack Binary Indexed Tree Segment Tree Heap (Priority Queue)Monotonic Stack

#14

Rank

#84HardFrequency: 69.6%

Largest Rectangle in Histogram

Array Stack Monotonic Stack Range Minimum/Maximum Query

#15

Rank

#636MediumFrequency: 67.4%

Exclusive Time of Functions

Array Stack

#16

Rank

#785HardFrequency: 66.8%

Basic Calculator III

#17

Rank

#385MediumFrequency: 65.5%

Mini Parser

Asked at Airbnb

#18

Rank

#758MediumFrequency: 63.7%

Convert Binary Search Tree to Sorted Doubly Linked List

Linked List Stack Tree Depth-First Search Binary Search Tree Binary Tree Doubly-Linked List

#19

Rank

#1320MediumFrequency: 63.5%

Remove All Adjacent Duplicates in String II

#20

Rank

#678MediumFrequency: 63.4%

Valid Parenthesis String

String Dynamic Programming Stack Greedy Bracket Sequences

#21

Rank

#1570EasyFrequency: 63.1%

Final Prices With a Special Discount in a Shop

#22

Rank

#1219MediumFrequency: 62.5%

Longest Well-Performing Interval

Array Hash Table Stack Monotonic Stack Prefix Sum

#23

Rank

#735MediumFrequency: 62.2%

Asteroid Collision

#24

Rank

#224HardFrequency: 61.8%

Basic Calculator

#25

Rank

#155MediumFrequency: 61.8%

Min Stack

Stack Design

#26

Rank

#272HardFrequency: 61.6%

Closest Binary Search Tree Value II

Two Pointers Stack Tree Depth-First Search Binary Search Tree Heap (Priority Queue)Binary Tree

#27

Rank

#739MediumFrequency: 61.4%

Daily Temperatures

#28

Rank

#173MediumFrequency: 60.9%

Binary Search Tree Iterator

Stack Tree Design Binary Search Tree Binary Tree Iterator

#29

Rank

#321HardFrequency: 59.8%

Create Maximum Number

Array Two Pointers Stack Greedy Monotonic Stack

#30

Rank

#1298MediumFrequency: 59.8%

Reverse Substrings Between Each Pair of Parentheses

#31

Rank

#943MediumFrequency: 59.8%

Sum of Subarray Minimums

#32

Rank

#143MediumFrequency: 59.3%

Reorder List

#33

Rank

#931HardFrequency: 57.5%

Maximum Frequency Stack

Hash Table Stack Design Ordered Set

#34

Rank

#234EasyFrequency: 57.2%

Palindrome Linked List

#35

Rank

#1633HardFrequency: 56.5%

Minimum Number of Increments on Subarrays to Form a Target Array

Array Dynamic Programming Stack Greedy Monotonic Stack

#36

Rank

#1128EasyFrequency: 55.6%

Remove All Adjacent Duplicates In String

#37

Rank

#3113MediumFrequency: 55.1%

Beautiful Towers II

#38

Rank

#3114MediumFrequency: 55.1%

Beautiful Towers I

#39

Rank

#496EasyFrequency: 54.7%

Next Greater Element I

Array Hash Table Stack Monotonic Stack

#40

Rank

#316MediumFrequency: 54.4%

Remove Duplicate Letters

#41

Rank

#503MediumFrequency: 54.1%

Next Greater Element II

#42

Rank

#1305HardFrequency: 52.9%

Number of Visible People in a Queue

#43

Rank

#32HardFrequency: 51.7%

Longest Valid Parentheses

String Dynamic Programming Stack Bracket Sequences

#44

Rank

#456MediumFrequency: 51.3%

132 Pattern

Asked at DoorDash

Array Binary Search Stack Monotonic Stack Ordered Set

#45

Rank

#85HardFrequency: 51.1%

Maximal Rectangle

Array Dynamic Programming Stack Matrix Monotonic Stack

#46

Rank

#341MediumFrequency: 51%

Flatten Nested List Iterator

Stack Tree Depth-First Search Design Queue Iterator

#47

Rank

#150MediumFrequency: 50.6%

Evaluate Reverse Polish Notation

Array Math Stack

#48

Rank

#1985MediumFrequency: 49.9%

Maximum Subarray Min-Product

Array Stack Monotonic Stack Prefix Sum Cartesian Tree

#49

Rank

#232EasyFrequency: 48.7%

Implement Queue using Stacks

#50

Rank

#536MediumFrequency: 47.5%

Construct Binary Tree from String

String Stack Tree Depth-First Search Binary Tree

#51

Rank

#2425MediumFrequency: 47.5%

Number of People That Can Be Seen in a Grid

Array Stack Matrix Monotonic Stack

#52

Rank

#937MediumFrequency: 45.8%

Online Stock Span

Stack Design Monotonic Stack Data Stream

#53

Rank

#402MediumFrequency: 45.1%

Remove K Digits

#54

Rank

#983MediumFrequency: 44.7%

Validate Stack Sequences

#55

Rank

#94EasyFrequency: 44.2%

Binary Tree Inorder Traversal

#56

Rank

#581MediumFrequency: 44%

Shortest Unsorted Continuous Subarray

Array Two Pointers Stack Greedy Sorting Monotonic Stack

#57

Rank

#2846HardFrequency: 43.2%

Robot Collisions

Array Stack Sorting Simulation

#58

Rank

#726HardFrequency: 43.2%

Number of Atoms

Hash Table String Stack Sorting

#59

Rank

#255MediumFrequency: 41.2%

Verify Preorder Sequence in Binary Search Tree

Array Stack Tree Binary Search Tree Recursion Monotonic Stack Binary Tree

#60

Rank

#2095MediumFrequency: 40.9%

Minimum Number of Swaps to Make the String Balanced

Two Pointers String Stack Greedy Bracket Sequences

#61

Rank

#114MediumFrequency: 40.5%

Flatten Binary Tree to Linked List

Linked List Stack Tree Depth-First Search Binary Tree

#62

Rank

#2368HardFrequency: 40.2%

Sum of Total Strength of Wizards

Array Stack Monotonic Stack Prefix Sum

#63

Rank

#2227MediumFrequency: 39.5%

Sum of Subarray Ranges

#64

Rank

#1002MediumFrequency: 39%

Maximum Width Ramp

Array Two Pointers Stack Monotonic Stack

#65

Rank

#225EasyFrequency: 38.2%

Implement Stack using Queues

#66

Rank

#445MediumFrequency: 38.2%

Add Two Numbers II

#67

Rank

#1050MediumFrequency: 37.4%

Construct Binary Search Tree from Preorder Traversal

Array Stack Tree Binary Search Tree Monotonic Stack Binary Tree

#68

Rank

#1756MediumFrequency: 37%

Minimum Deletions to Make String Balanced

String Dynamic Programming Stack

#69

Rank

#1017HardFrequency: 35.8%

Odd Even Jump

Array Dynamic Programming Stack Sorting Monotonic Stack Ordered Set

#70

Rank

#2520MediumFrequency: 35.6%

Using a Robot to Print the Lexicographically Smallest String

Hash Table String Stack Greedy

#71

Rank

#1159MediumFrequency: 35.1%

Smallest Subsequence of Distinct Characters

#72

Rank

#1076MediumFrequency: 35%

Brace Expansion

String Backtracking Stack Breadth-First Search Sorting

#73

Rank

#874EasyFrequency: 34.8%

Backspace String Compare

Two Pointers String Stack Simulation

#74

Rank

#1078EasyFrequency: 33.7%

Remove Outermost Parentheses

#75

Rank

#2307HardFrequency: 33.5%

Replace Non-Coprime Numbers in Array

Array Math Stack Number Theory Least Common Multiple Greatest Common Divisor

#76

Rank

#886MediumFrequency: 33%

Score of Parentheses

#77

Rank

#1072MediumFrequency: 32.8%

Next Greater Node In Linked List

Array Linked List Stack Monotonic Stack

#78

Rank

#1497MediumFrequency: 32.4%

Design a Stack With Increment Operation

Array Stack Design

#79

Rank

#2470MediumFrequency: 32.3%

Removing Stars From a String

#80

Rank

#883MediumFrequency: 31.8%

Car Fleet

#81

Rank

#4000MediumFrequency: 31.3%

Count Bowl Subarrays

#82

Rank

#2021MediumFrequency: 31.3%

Remove All Occurrences of a Substring

#83

Rank

#1802EasyFrequency: 31.1%

Number of Students Unable to Eat Lunch

Array Stack Queue Simulation

#84

Rank

#1582MediumFrequency: 29.5%

Design Browser History

Array Linked List Stack Design Doubly-Linked List Data Stream

#85

Rank

#736HardFrequency: 29.5%

Parse Lisp Expression

Hash Table String Stack Recursion

#86

Rank

#1048MediumFrequency: 29.3%

Clumsy Factorial

Math Stack Simulation

#87

Rank

#3454HardFrequency: 29.3%

Minimum Operations to Make Array Equal to Target

Array Dynamic Programming Stack Greedy Monotonic Stack

#88

Rank

#2490HardFrequency: 29.1%

Maximum Number of Books You Can Take

#89

Rank

#780MediumFrequency: 28.1%

Max Chunks To Make Sorted

#90

Rank

#2389HardFrequency: 28.1%

Design a Text Editor

Linked List String Stack Design Simulation Doubly-Linked List

#91

Rank

#682EasyFrequency: 27.8%

Baseball Game

#92

Rank

#1768MediumFrequency: 27.8%

Design an Expression Tree With Evaluate Function

Array Math Stack Tree Design Binary Tree

#93

Rank

#2456MediumFrequency: 27.8%

Construct Smallest Number From DI String

String Backtracking Stack Greedy

#94

Rank

#2111MediumFrequency: 27.8%

Binary Searchable Numbers in an Unsorted Array

#95

Rank

#779HardFrequency: 27.7%

Max Chunks To Make Sorted II

#96

Rank

#2485MediumFrequency: 27.7%

Finding the Number of Visible Mountains

#97

Rank

#3445MediumFrequency: 27.7%

Lexicographically Minimum String After Removing Stars

Hash Table String Stack Greedy Heap (Priority Queue)

#98

Rank

#591HardFrequency: 27.3%

Tag Validator

#99

Rank

#654MediumFrequency: 27.3%

Maximum Binary Tree

Array Divide and Conquer Stack Tree Monotonic Stack Binary Tree Cartesian Tree

#100

Rank

#1355MediumFrequency: 27.3%

Minimum Deletions to Make Array Beautiful

Array Stack Greedy

#101

Rank

#4222HardFrequency: 27.3%

Count Good Subarrays

Array Stack Bit Manipulation Monotonic Stack

#102

Rank

#144EasyFrequency: 27.2%

Binary Tree Preorder Traversal

#103

Rank

#1818MediumFrequency: 27.2%

Maximum Score From Removing Substrings

String Stack Greedy

#104

Rank

#1737EasyFrequency: 26.7%

Maximum Nesting Depth of the Parentheses

#105

Rank

#1679MediumFrequency: 26.5%

Shortest Subarray to be Removed to Make Array Sorted

Array Two Pointers Binary Search Stack Monotonic Stack

#106

Rank

#1628MediumFrequency: 26.3%

Count Submatrices With All Ones

Array Dynamic Programming Stack Matrix Monotonic Stack

#107

Rank

#1666EasyFrequency: 26.3%

Make The String Great

#108

Rank

#388MediumFrequency: 26.3%

Longest Absolute File Path

#109

Rank

#1552MediumFrequency: 25.4%

Build an Array With Stack Operations

#110

Rank

#1792MediumFrequency: 25.4%

Find the Most Competitive Subsequence

#111

Rank

#2236MediumFrequency: 25.1%

Maximum Twin Sum of a Linked List

Linked List Two Pointers Stack

#112

Rank

#1729MediumFrequency: 25.1%

Binary Search Tree Iterator II

Stack Tree Design Binary Search Tree Binary Tree Iterator

#113

Rank

#3211HardFrequency: 24.6%

Find Maximum Non-decreasing Array Length

Array Binary Search Dynamic Programming Stack Queue Monotonic Stack Prefix Sum Monotonic Queue

#114

Rank

#3674HardFrequency: 24.4%

Count Non-Decreasing Subarrays After K Operations

Array Stack Segment Tree Queue Sliding Window Monotonic Stack Monotonic Queue

#115

Rank

#1150MediumFrequency: 23.6%

Two Sum BSTs

Two Pointers Binary Search Stack Tree Depth-First Search Binary Search Tree Binary Tree

#116

Rank

#2573MediumFrequency: 23.6%

Remove Nodes From Linked List

Linked List Stack Recursion Monotonic Stack

#117

Rank

#3447EasyFrequency: 23.3%

Clear Digits

#118

Rank

#1197HardFrequency: 21.9%

Parsing A Boolean Expression

#119

Rank

#2374MediumFrequency: 21.5%

Steps to Make Array Non-decreasing

Array Linked List Dynamic Programming Stack Monotonic Stack Simulation

#120

Rank

#145EasyFrequency: 20.9%

Binary Tree Postorder Traversal

#121

Rank

#331MediumFrequency: 20.9%

Verify Preorder Serialization of a Binary Tree

#122

Rank

#1918HardFrequency: 20.9%

Maximum Score of a Good Subarray

Array Two Pointers Binary Search Stack Monotonic Stack Cartesian Tree

#123

Rank

#2123MediumFrequency: 20.9%

The Number of Weak Characters in the Game

#124

Rank

#1902HardFrequency: 20.9%

Car Fleet II

Array Math Stack Heap (Priority Queue)Monotonic Stack

#125

Rank

#1736HardFrequency: 20%

Build Binary Expression Tree From Infix Expression

#126

Rank

#2056MediumFrequency: 20%

Jump Game VIII

Array Dynamic Programming Stack Graph Theory Monotonic Stack Shortest Path

#127

Rank

#2072MediumFrequency: 20%

Maximum of Minimum Values in All Subarrays

Array Stack Monotonic Stack Cartesian Tree

#128

Rank

#2871MediumFrequency: 20%

Double a Number Represented as a Linked List

#129

Rank

#3088MediumFrequency: 20%

Maximal Range That Each Element Is Maximum in It

#130

Rank

#3382HardFrequency: 20%

Find the Number of Subarrays Where Boundary Elements Are Maximum

#131

Rank

#1188HardFrequency: 18%

Brace Expansion II

Hash Table String Backtracking Stack Breadth-First Search Sorting

#132

Rank

#3158MediumFrequency: 18%

Maximum Length of Semi-Decreasing Subarrays

#133

Rank

#2221MediumFrequency: 17%

Check if a Parentheses String Can Be Valid

#134

Rank

#484MediumFrequency: 16.4%

Find Permutation

Array String Stack Greedy

#135

Rank

#2008HardFrequency: 16.4%

Minimum Cost to Change the Final Value of Expression

Math String Dynamic Programming Stack

#136

Rank

#3954MediumFrequency: 15.7%

Maximum Balanced Shipments

Array Dynamic Programming Stack Greedy Monotonic Stack

#137

Rank

#2128EasyFrequency: 13.2%

Reverse Prefix of Word

Two Pointers String Stack

#138

Rank

#1648MediumFrequency: 11.4%

Minimum Insertions to Balance a Parentheses String

#139

Rank

#1720EasyFrequency: 11.4%

Crawler Log Folder

Array String Stack

#140

Rank

#933EasyFrequency: 10.5%

Increasing Order Search Tree

Stack Tree Depth-First Search Binary Search Tree Binary Tree

#141

Rank

#1228MediumFrequency: 10.5%

Minimum Cost Tree From Leaf Values

Array Dynamic Programming Stack Greedy Monotonic Stack Cartesian Tree

#142

Rank

#2800EasyFrequency: 10.5%

Minimum String Length After Removing Substrings

#143

Rank

#3001HardFrequency: 10.5%

Apply Operations to Maximize Score

Array Math Stack Greedy Sorting Monotonic Stack Number Theory

#144

Rank

#3834MediumFrequency: 10.5%

Minimum Operations to Convert All Elements to Zero

Array Hash Table Stack Greedy Monotonic Stack

#145

Rank

#776EasyFrequency: 10.3%

N-ary Tree Postorder Traversal

#146

Rank

#781HardFrequency: 8.1%

Basic Calculator IV

Hash Table Math String Stack Recursion

#147

Rank

#3738MediumFrequency: 8.1%

Make Array Non-decreasing

#148

Rank

#1208MediumFrequency: 8.1%

Maximum Nesting Depth of Two Valid Parentheses Strings

#149

Rank

#3860MediumFrequency: 8%

Resulting String After Adjacent Removals

#150

Rank

#916MediumFrequency: 8%

Decoded String at Index

#151

Rank

#2736MediumFrequency: 7.3%

Minimum Additions to Make Valid String

String Dynamic Programming Stack Greedy

#152

Rank

#1270HardFrequency: 7.2%

Dinner Plate Stacks

Hash Table Stack Design Heap (Priority Queue)

#153

Rank

#775EasyFrequency: 7.2%

N-ary Tree Preorder Traversal

#154

Rank

#2317MediumFrequency: 5.5%

Count Collisions on a Road

#155

Rank

#488HardFrequency: 5.5%

Zuma Game

String Dynamic Programming Stack Breadth-First Search Memoization

#156

Rank

#2657HardFrequency: 5%

Minimum Time to Complete All Tasks

Array Binary Search Stack Greedy Sorting

#157

Rank

#3634MediumFrequency: 5%

Find Mirror Score of a String

Hash Table String Stack Simulation

#158

Rank

#4140HardFrequency: 5%

Evaluate Valid Expressions

Hash Table Math String Divide and Conquer Stack

#159

Rank

#4086HardFrequency: 5%

Lexicographically Smallest String After Deleting Duplicate Characters

Hash Table String Stack Greedy Monotonic Stack

#160

Rank

#2549HardFrequency: 5%

Next Greater Element IV

Array Binary Search Stack Sorting Heap (Priority Queue)Monotonic Stack

#161

Rank

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Stack Interview Questions

Master 161 stack problems frequently asked in technical interviews. These questions test your understanding of stackconcepts and are essential for coding interview success.

161

Total Problems

Easy

Medium

Hard

Minimum Remove to Make Valid Parentheses

Rank

#716HardFrequency: 100%

Max Stack

Linked List Stack Design Doubly-Linked List Ordered Set

Rank

#364MediumFrequency: 95.4%

Nested List Weight Sum II

Stack Depth-First Search Breadth-First Search

Rank

#227MediumFrequency: 89.3%

Basic Calculator II

Math String Stack

Rank

#42HardFrequency: 88%

Trapping Rain Water

Array Two Pointers Dynamic Programming Stack Monotonic Stack

Rank

#71MediumFrequency: 83.7%

Simplify Path

Rank

#1909MediumFrequency: 82.6%

Buildings With an Ocean View

Rank

#20EasyFrequency: 79%

Valid Parentheses

Rank

#2147HardFrequency: 76.6%

The Score of Students Solving Math Expression

Array Hash Table Math String Dynamic Programming Stack Memoization

Rank

#2667HardFrequency: 76%

Maximum Frequency Score of a Subarray

Array Hash Table Math Stack Sliding Window

#10

Rank

#394MediumFrequency: 75.8%

Decode String

#11

Rank

#957MediumFrequency: 71.8%

Minimum Add to Make Parentheses Valid

#12

Rank

#2419HardFrequency: 69.8%

Subarray With Elements Greater Than Varying Threshold

Array Stack Union-Find Monotonic Stack

#13

Rank

#3181HardFrequency: 69.8%

Find Building Where Alice and Bob Can Meet

Array Binary Search Stack Binary Indexed Tree Segment Tree Heap (Priority Queue)Monotonic Stack

#14

Rank

#84HardFrequency: 69.6%

Largest Rectangle in Histogram

Array Stack Monotonic Stack Range Minimum/Maximum Query

#15

Rank

#636MediumFrequency: 67.4%

Exclusive Time of Functions

Array Stack

#16

Rank

#785HardFrequency: 66.8%

Basic Calculator III

#17

Rank

#385MediumFrequency: 65.5%

Mini Parser

Asked at Airbnb

#18

Rank

#758MediumFrequency: 63.7%

Convert Binary Search Tree to Sorted Doubly Linked List

Linked List Stack Tree Depth-First Search Binary Search Tree Binary Tree Doubly-Linked List

#19

Rank

#1320MediumFrequency: 63.5%

Remove All Adjacent Duplicates in String II

#20

Rank

#678MediumFrequency: 63.4%

Valid Parenthesis String

String Dynamic Programming Stack Greedy Bracket Sequences

#21

Rank

#1570EasyFrequency: 63.1%

Final Prices With a Special Discount in a Shop

#22

Rank

#1219MediumFrequency: 62.5%

Longest Well-Performing Interval

Array Hash Table Stack Monotonic Stack Prefix Sum

#23

Rank

#735MediumFrequency: 62.2%

Asteroid Collision

#24

Rank

#224HardFrequency: 61.8%

Basic Calculator

#25

Rank

#155MediumFrequency: 61.8%

Min Stack

Stack Design

#26

Rank

#272HardFrequency: 61.6%

Closest Binary Search Tree Value II

Two Pointers Stack Tree Depth-First Search Binary Search Tree Heap (Priority Queue)Binary Tree

#27

Rank

#739MediumFrequency: 61.4%

Daily Temperatures

#28

Rank

#173MediumFrequency: 60.9%

Binary Search Tree Iterator

Stack Tree Design Binary Search Tree Binary Tree Iterator

#29

Rank

#321HardFrequency: 59.8%

Create Maximum Number

Array Two Pointers Stack Greedy Monotonic Stack

#30

Rank

#1298MediumFrequency: 59.8%

Reverse Substrings Between Each Pair of Parentheses

#31

Rank

#943MediumFrequency: 59.8%

Sum of Subarray Minimums

#32

Rank

#143MediumFrequency: 59.3%

Reorder List

#33

Rank

#931HardFrequency: 57.5%

Maximum Frequency Stack

Hash Table Stack Design Ordered Set

#34

Rank

#234EasyFrequency: 57.2%

Palindrome Linked List

#35

Rank

#1633HardFrequency: 56.5%

Minimum Number of Increments on Subarrays to Form a Target Array

Array Dynamic Programming Stack Greedy Monotonic Stack

#36

Rank

#1128EasyFrequency: 55.6%

Remove All Adjacent Duplicates In String

#37

Rank

#3113MediumFrequency: 55.1%

Beautiful Towers II

#38

Rank

#3114MediumFrequency: 55.1%

Beautiful Towers I

#39

Rank

#496EasyFrequency: 54.7%

Next Greater Element I

Array Hash Table Stack Monotonic Stack

#40

Rank

#316MediumFrequency: 54.4%

Remove Duplicate Letters

#41

Rank

#503MediumFrequency: 54.1%

Next Greater Element II

#42

Rank

#1305HardFrequency: 52.9%

Number of Visible People in a Queue

#43

Rank

#32HardFrequency: 51.7%

Longest Valid Parentheses

String Dynamic Programming Stack Bracket Sequences

#44

Rank

#456MediumFrequency: 51.3%

132 Pattern

Asked at DoorDash

Array Binary Search Stack Monotonic Stack Ordered Set

#45

Rank

#85HardFrequency: 51.1%

Maximal Rectangle

Array Dynamic Programming Stack Matrix Monotonic Stack

#46

Rank

#341MediumFrequency: 51%

Flatten Nested List Iterator

Stack Tree Depth-First Search Design Queue Iterator

#47

Rank

#150MediumFrequency: 50.6%

Evaluate Reverse Polish Notation

Array Math Stack

#48

Rank

#1985MediumFrequency: 49.9%

Maximum Subarray Min-Product

Array Stack Monotonic Stack Prefix Sum Cartesian Tree

#49

Rank

#232EasyFrequency: 48.7%

Implement Queue using Stacks

#50

Rank

#536MediumFrequency: 47.5%

Construct Binary Tree from String

String Stack Tree Depth-First Search Binary Tree

#51

Rank

#2425MediumFrequency: 47.5%

Number of People That Can Be Seen in a Grid

Array Stack Matrix Monotonic Stack

#52

Rank

#937MediumFrequency: 45.8%

Online Stock Span

Stack Design Monotonic Stack Data Stream

#53

Rank

#402MediumFrequency: 45.1%

Remove K Digits

#54

Rank

#983MediumFrequency: 44.7%

Validate Stack Sequences

#55

Rank

#94EasyFrequency: 44.2%

Binary Tree Inorder Traversal

#56

Rank

#581MediumFrequency: 44%

Shortest Unsorted Continuous Subarray

Array Two Pointers Stack Greedy Sorting Monotonic Stack

#57

Rank

#2846HardFrequency: 43.2%

Robot Collisions

Array Stack Sorting Simulation

#58

Rank

#726HardFrequency: 43.2%

Number of Atoms

Hash Table String Stack Sorting

#59

Rank

#255MediumFrequency: 41.2%

Verify Preorder Sequence in Binary Search Tree

Array Stack Tree Binary Search Tree Recursion Monotonic Stack Binary Tree

#60

Rank

#2095MediumFrequency: 40.9%

Minimum Number of Swaps to Make the String Balanced

Two Pointers String Stack Greedy Bracket Sequences

#61

Rank

#114MediumFrequency: 40.5%

Flatten Binary Tree to Linked List

Linked List Stack Tree Depth-First Search Binary Tree

#62

Rank

#2368HardFrequency: 40.2%

Sum of Total Strength of Wizards

Array Stack Monotonic Stack Prefix Sum

#63

Rank

#2227MediumFrequency: 39.5%

Sum of Subarray Ranges

#64

Rank

#1002MediumFrequency: 39%

Maximum Width Ramp

Array Two Pointers Stack Monotonic Stack

#65

Rank

#225EasyFrequency: 38.2%

Implement Stack using Queues

#66

Rank

#445MediumFrequency: 38.2%

Add Two Numbers II

#67

Rank

#1050MediumFrequency: 37.4%

Construct Binary Search Tree from Preorder Traversal

Array Stack Tree Binary Search Tree Monotonic Stack Binary Tree

#68

Rank

#1756MediumFrequency: 37%

Minimum Deletions to Make String Balanced

String Dynamic Programming Stack

#69

Rank

#1017HardFrequency: 35.8%

Odd Even Jump

Array Dynamic Programming Stack Sorting Monotonic Stack Ordered Set

#70

Rank

#2520MediumFrequency: 35.6%

Using a Robot to Print the Lexicographically Smallest String

Hash Table String Stack Greedy

#71

Rank

#1159MediumFrequency: 35.1%

Smallest Subsequence of Distinct Characters

#72

Rank

#1076MediumFrequency: 35%

Brace Expansion

String Backtracking Stack Breadth-First Search Sorting

#73

Rank

#874EasyFrequency: 34.8%

Backspace String Compare

Two Pointers String Stack Simulation

#74

Rank

#1078EasyFrequency: 33.7%

Remove Outermost Parentheses

#75

Rank

#2307HardFrequency: 33.5%

Replace Non-Coprime Numbers in Array

Array Math Stack Number Theory Least Common Multiple Greatest Common Divisor

#76

Rank

#886MediumFrequency: 33%

Score of Parentheses

#77

Rank

#1072MediumFrequency: 32.8%

Next Greater Node In Linked List

Array Linked List Stack Monotonic Stack

#78

Rank

#1497MediumFrequency: 32.4%

Design a Stack With Increment Operation

Array Stack Design

#79

Rank

#2470MediumFrequency: 32.3%

Removing Stars From a String

#80

Rank

#883MediumFrequency: 31.8%

Car Fleet

#81

Rank

#4000MediumFrequency: 31.3%

Count Bowl Subarrays

#82

Rank

#2021MediumFrequency: 31.3%

Remove All Occurrences of a Substring

#83

Rank

#1802EasyFrequency: 31.1%

Number of Students Unable to Eat Lunch

Array Stack Queue Simulation

#84

Rank

#1582MediumFrequency: 29.5%

Design Browser History

Array Linked List Stack Design Doubly-Linked List Data Stream

#85

Rank

#736HardFrequency: 29.5%

Parse Lisp Expression

Hash Table String Stack Recursion

#86

Rank

#1048MediumFrequency: 29.3%

Clumsy Factorial

Math Stack Simulation

#87

Rank

#3454HardFrequency: 29.3%

Minimum Operations to Make Array Equal to Target

Array Dynamic Programming Stack Greedy Monotonic Stack

#88

Rank

#2490HardFrequency: 29.1%

Maximum Number of Books You Can Take

#89

Rank

#780MediumFrequency: 28.1%

Max Chunks To Make Sorted

#90

Rank

#2389HardFrequency: 28.1%

Design a Text Editor

Linked List String Stack Design Simulation Doubly-Linked List

#91

Rank

#682EasyFrequency: 27.8%

Baseball Game

#92

Rank

#1768MediumFrequency: 27.8%

Design an Expression Tree With Evaluate Function

Array Math Stack Tree Design Binary Tree

#93

Rank

#2456MediumFrequency: 27.8%

Construct Smallest Number From DI String

String Backtracking Stack Greedy

#94

Rank

#2111MediumFrequency: 27.8%

Binary Searchable Numbers in an Unsorted Array

#95

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#779HardFrequency: 27.7%

Max Chunks To Make Sorted II

#96

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#2485MediumFrequency: 27.7%

Finding the Number of Visible Mountains

#97

Rank

#3445MediumFrequency: 27.7%

Lexicographically Minimum String After Removing Stars

Hash Table String Stack Greedy Heap (Priority Queue)

#98

Rank

#591HardFrequency: 27.3%

Tag Validator

#99

Rank

#654MediumFrequency: 27.3%

Maximum Binary Tree

Array Divide and Conquer Stack Tree Monotonic Stack Binary Tree Cartesian Tree

#100

Rank

#1355MediumFrequency: 27.3%

Minimum Deletions to Make Array Beautiful

Array Stack Greedy

#101

Rank

#4222HardFrequency: 27.3%

Count Good Subarrays

Array Stack Bit Manipulation Monotonic Stack

#102

Rank

#144EasyFrequency: 27.2%

Binary Tree Preorder Traversal

#103

Rank

#1818MediumFrequency: 27.2%

Maximum Score From Removing Substrings

String Stack Greedy

#104

Rank

#1737EasyFrequency: 26.7%

Maximum Nesting Depth of the Parentheses

#105

Rank

#1679MediumFrequency: 26.5%

Shortest Subarray to be Removed to Make Array Sorted

Array Two Pointers Binary Search Stack Monotonic Stack

#106

Rank

#1628MediumFrequency: 26.3%

Count Submatrices With All Ones

Array Dynamic Programming Stack Matrix Monotonic Stack

#107

Rank

#1666EasyFrequency: 26.3%

Make The String Great

#108

Rank

#388MediumFrequency: 26.3%

Longest Absolute File Path

#109

Rank

#1552MediumFrequency: 25.4%

Build an Array With Stack Operations

#110

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#1792MediumFrequency: 25.4%

Find the Most Competitive Subsequence

#111

Rank

#2236MediumFrequency: 25.1%

Maximum Twin Sum of a Linked List

Linked List Two Pointers Stack

#112

Rank

#1729MediumFrequency: 25.1%

Binary Search Tree Iterator II

Stack Tree Design Binary Search Tree Binary Tree Iterator

#113

Rank

#3211HardFrequency: 24.6%

Find Maximum Non-decreasing Array Length

Array Binary Search Dynamic Programming Stack Queue Monotonic Stack Prefix Sum Monotonic Queue

#114

Rank

#3674HardFrequency: 24.4%

Count Non-Decreasing Subarrays After K Operations

Array Stack Segment Tree Queue Sliding Window Monotonic Stack Monotonic Queue

#115

Rank

#1150MediumFrequency: 23.6%

Two Sum BSTs

Two Pointers Binary Search Stack Tree Depth-First Search Binary Search Tree Binary Tree

#116

Rank

#2573MediumFrequency: 23.6%

Remove Nodes From Linked List

Linked List Stack Recursion Monotonic Stack

#117

Rank

#3447EasyFrequency: 23.3%

Clear Digits

#118

Rank

#1197HardFrequency: 21.9%

Parsing A Boolean Expression

#119

Rank

#2374MediumFrequency: 21.5%

Steps to Make Array Non-decreasing

Array Linked List Dynamic Programming Stack Monotonic Stack Simulation

#120

Rank

#145EasyFrequency: 20.9%

Binary Tree Postorder Traversal

#121

Rank

#331MediumFrequency: 20.9%

Verify Preorder Serialization of a Binary Tree

#122

Rank

#1918HardFrequency: 20.9%

Maximum Score of a Good Subarray

Array Two Pointers Binary Search Stack Monotonic Stack Cartesian Tree

#123

Rank

#2123MediumFrequency: 20.9%

The Number of Weak Characters in the Game

#124

Rank

#1902HardFrequency: 20.9%

Car Fleet II

Array Math Stack Heap (Priority Queue)Monotonic Stack

#125

Rank

#1736HardFrequency: 20%

Build Binary Expression Tree From Infix Expression

#126

Rank

#2056MediumFrequency: 20%

Jump Game VIII

Array Dynamic Programming Stack Graph Theory Monotonic Stack Shortest Path

#127

Rank

#2072MediumFrequency: 20%

Maximum of Minimum Values in All Subarrays

Array Stack Monotonic Stack Cartesian Tree

#128

Rank

#2871MediumFrequency: 20%

Double a Number Represented as a Linked List

#129

Rank

#3088MediumFrequency: 20%

Maximal Range That Each Element Is Maximum in It

#130

Rank

#3382HardFrequency: 20%

Find the Number of Subarrays Where Boundary Elements Are Maximum

#131

Rank

#1188HardFrequency: 18%

Brace Expansion II

Hash Table String Backtracking Stack Breadth-First Search Sorting

#132

Rank

#3158MediumFrequency: 18%

Maximum Length of Semi-Decreasing Subarrays

#133

Rank

#2221MediumFrequency: 17%

Check if a Parentheses String Can Be Valid

#134

Rank

#484MediumFrequency: 16.4%

Find Permutation

Array String Stack Greedy

#135

Rank

#2008HardFrequency: 16.4%

Minimum Cost to Change the Final Value of Expression

Math String Dynamic Programming Stack

#136

Rank

#3954MediumFrequency: 15.7%

Maximum Balanced Shipments

Array Dynamic Programming Stack Greedy Monotonic Stack

#137

Rank

#2128EasyFrequency: 13.2%

Reverse Prefix of Word

Two Pointers String Stack

#138

Rank

#1648MediumFrequency: 11.4%

Minimum Insertions to Balance a Parentheses String

#139

Rank

#1720EasyFrequency: 11.4%

Crawler Log Folder

Array String Stack

#140

Rank

#933EasyFrequency: 10.5%

Increasing Order Search Tree

Stack Tree Depth-First Search Binary Search Tree Binary Tree

#141

Rank

#1228MediumFrequency: 10.5%

Minimum Cost Tree From Leaf Values

Array Dynamic Programming Stack Greedy Monotonic Stack Cartesian Tree

#142

Rank

#2800EasyFrequency: 10.5%

Minimum String Length After Removing Substrings

#143

Rank

#3001HardFrequency: 10.5%

Apply Operations to Maximize Score

Array Math Stack Greedy Sorting Monotonic Stack Number Theory

#144

Rank

#3834MediumFrequency: 10.5%

Minimum Operations to Convert All Elements to Zero

Array Hash Table Stack Greedy Monotonic Stack

#145

Rank

#776EasyFrequency: 10.3%

N-ary Tree Postorder Traversal

#146

Rank

#781HardFrequency: 8.1%

Basic Calculator IV

Hash Table Math String Stack Recursion

#147

Rank

#3738MediumFrequency: 8.1%

Make Array Non-decreasing

#148

Rank

#1208MediumFrequency: 8.1%

Maximum Nesting Depth of Two Valid Parentheses Strings

#149

Rank

#3860MediumFrequency: 8%

Resulting String After Adjacent Removals

#150

Rank

#916MediumFrequency: 8%

Decoded String at Index

#151

Rank

#2736MediumFrequency: 7.3%

Minimum Additions to Make Valid String

String Dynamic Programming Stack Greedy

#152

Rank

#1270HardFrequency: 7.2%

Dinner Plate Stacks

Hash Table Stack Design Heap (Priority Queue)

#153

Rank

#775EasyFrequency: 7.2%

N-ary Tree Preorder Traversal

#154

Rank

#2317MediumFrequency: 5.5%

Count Collisions on a Road

#155

Rank

#488HardFrequency: 5.5%

Zuma Game

String Dynamic Programming Stack Breadth-First Search Memoization

#156

Rank

#2657HardFrequency: 5%

Minimum Time to Complete All Tasks

Array Binary Search Stack Greedy Sorting

#157

Rank

#3634MediumFrequency: 5%

Find Mirror Score of a String

Hash Table String Stack Simulation

#158

Rank

#4140HardFrequency: 5%

Evaluate Valid Expressions

Hash Table Math String Divide and Conquer Stack

#159

Rank

#4086HardFrequency: 5%

Lexicographically Smallest String After Deleting Duplicate Characters

Hash Table String Stack Greedy Monotonic Stack

#160

Rank

#2549HardFrequency: 5%

Next Greater Element IV