Union Find Interview Questions

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

Rank

#305HardFrequency: 89.9%

Number of Islands II

Array Hash Table Union-Find

Rank

#694MediumFrequency: 86.6%

Number of Distinct Islands

Array Hash Table Depth-First Search Breadth-First Search Union-Find Sorting Matrix Hash Function

Rank

#854HardFrequency: 72.8%

Making A Large Island

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

Rank

#128MediumFrequency: 70.7%

Longest Consecutive Sequence

Array Hash Table Union-Find

Rank

#399MediumFrequency: 70.2%

Evaluate Division

Array String Depth-First Search Breadth-First Search Union-Find Graph Theory Shortest Path Bellman–Ford Algorithm Floyd–Warshall Algorithm

Rank

#2419HardFrequency: 69.8%

Subarray With Elements Greater Than Varying Threshold

Array Stack Union-Find Monotonic Stack

Rank

#960HardFrequency: 66.4%

Minimize Malware Spread

Asked at Salesforce

Array Hash Table Depth-First Search Breadth-First Search Union-Find Graph Theory

Rank

#2726HardFrequency: 65.2%

Minimum Reverse Operations

Asked at Infosys

Array Hash Table Breadth-First Search Union-Find Ordered Set

Rank

#3863MediumFrequency: 64.9%

Power Grid Maintenance

Asked at Salesforce

Array Hash Table Depth-First Search Breadth-First Search Union-Find Graph Theory Heap (Priority Queue)Ordered Set

#10

Rank

#1085MediumFrequency: 63.1%

The Earliest Moment When Everyone Become Friends

Array Union-Find Prefix Sum Ordered Set

Array Union-Find Sorting

#11

Rank

#2466HardFrequency: 62.5%

Maximum Segment Sum After Removals

Asked at Infosys

#12

Rank

#3881MediumFrequency: 61.5%

Minimize Maximum Component Cost

Asked at Salesforce

Binary Search Union-Find Graph Theory Sorting

#13

Rank

#721MediumFrequency: 61.4%

Accounts Merge

Array Hash Table String Depth-First Search Breadth-First Search Union-Find Sorting

#14

Rank

#695MediumFrequency: 59.3%

Max Area of Island

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

#15

Rank

#2583HardFrequency: 57.5%

Divide Nodes Into the Maximum Number of Groups

Depth-First Search Breadth-First Search Union-Find Graph Theory

#16

Rank

#1308MediumFrequency: 57%

Smallest String With Swaps

Asked at PayPal

Array Hash Table String Depth-First Search Breadth-First Search Union-Find Sorting

#17

Rank

#922MediumFrequency: 54.4%

Possible Bipartition

Depth-First Search Breadth-First Search Union-Find Graph Theory Graph Coloring Bipartite Graph

#18

Rank

#547MediumFrequency: 50.7%

Number of Provinces

Depth-First Search Breadth-First Search Union-Find Graph Theory

#19

Rank

#999MediumFrequency: 49.9%

Regions Cut By Slashes

Array Hash Table Depth-First Search Breadth-First Search Union-Find Matrix Planar Graph

#20

Rank

#1701HardFrequency: 47.5%

Remove Max Number of Edges to Keep Graph Fully Traversable

Union-Find Graph Theory

#21

Rank

#2065HardFrequency: 47.5%

Check for Contradictions in Equations

Array String Depth-First Search Union-Find Graph Theory

#22

Rank

#130MediumFrequency: 46.9%

Surrounded Regions

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

#23

Rank

#261MediumFrequency: 44.7%

Graph Valid Tree

Asked at LinkedIn

Depth-First Search Breadth-First Search Union-Find Graph Theory

#24

Rank

#1706MediumFrequency: 44%

Min Cost to Connect All Points

Array Union-Find Graph Theory Minimum Spanning Tree Prim's Algorithm Kruskal's Algorithm Borůvka's Algorithm

#25

Rank

#323MediumFrequency: 42.2%

Number of Connected Components in an Undirected Graph

Asked at LinkedIn

Depth-First Search Breadth-First Search Union-Find Graph Theory

#26

Rank

#2914MediumFrequency: 41.6%

Find the Safest Path in a Grid

Array Binary Search Breadth-First Search Union-Find Heap (Priority Queue)Matrix

#27

Rank

#1442MediumFrequency: 40.9%

Number of Operations to Make Network Connected

Asked at PayPal

Depth-First Search Breadth-First Search Union-Find Graph Theory

#28

Rank

#794HardFrequency: 40%

Swim in Rising Water

Array Binary Search Depth-First Search Breadth-First Search Union-Find Minimax Heap (Priority Queue)Matrix Dijkstra's Algorithm

#29

Rank

#2588HardFrequency: 37.9%

Maximum Number of Points From Grid Queries

Array Two Pointers Breadth-First Search Union-Find Sorting Heap (Priority Queue)Matrix

#30

Rank

#1753MediumFrequency: 37.3%

Path With Minimum Effort

Array Binary Search Depth-First Search Breadth-First Search Union-Find Heap (Priority Queue)Matrix Dijkstra's Algorithm

#31

Rank

#801MediumFrequency: 34.2%

Is Graph Bipartite?

Depth-First Search Breadth-First Search Union-Find Graph Theory Graph Coloring Bipartite Graph

#32

Rank

#2035MediumFrequency: 34.2%

Count Sub Islands

Asked at DoorDash

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

#33

Rank

#869HardFrequency: 34.2%

Similar String Groups

Asked at DoorDash

Array Hash Table String Depth-First Search Breadth-First Search Union-Find

#34

Rank

#684MediumFrequency: 33.7%

Redundant Connection

Depth-First Search Breadth-First Search Union-Find Graph Theory

#35

Rank

#1613HardFrequency: 33.5%

Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree

Union-Find Graph Theory Sorting Minimum Spanning Tree Strongly Connected Component Prim's Algorithm Kruskal's Algorithm Borůvka's Algorithm

#36

Rank

#1380MediumFrequency: 33.3%

Number of Closed Islands

Asked at Oracle

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

#37

Rank

#2121EasyFrequency: 32.8%

Find if Path Exists in Graph

Asked at Microsoft

Depth-First Search Breadth-First Search Union-Find Graph Theory

#38

Rank

#3838MediumFrequency: 32.4%

Path Existence Queries in a Graph I

Array Hash Table Binary Search Union-Find Graph Theory

#39

Rank

#3983HardFrequency: 31.3%

Minimum Operations to Equalize Binary String

Asked at Infosys

Math String Breadth-First Search Union-Find Ordered Set

#40

Rank

#984MediumFrequency: 29.1%

Most Stones Removed with Same Row or Column

Hash Table Depth-First Search Union-Find Graph Theory Bipartite Graph

#41

Rank

#2403MediumFrequency: 27.8%

Count Unreachable Pairs of Nodes in an Undirected Graph

Depth-First Search Breadth-First Search Union-Find Graph Theory

#42

Rank

#1223HardFrequency: 27.8%

Graph Connectivity With Threshold

Array Math Union-Find Number Theory

#43

Rank

#1073MediumFrequency: 27.2%

Number of Enclaves

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

#44

Rank

#2125HardFrequency: 26.5%

GCD Sort of an Array

Array Math Union-Find Sorting Number Theory Prime Factorization Euclidean Algorithm Greatest Common Divisor

#45

Rank

#1099MediumFrequency: 25.4%

Path With Maximum Minimum Value

Array Binary Search Depth-First Search Breadth-First Search Union-Find Heap (Priority Queue)Matrix Dijkstra's Algorithm

#46

Rank

#711HardFrequency: 25.1%

Number of Distinct Islands II

Array Hash Table Depth-First Search Breadth-First Search Union-Find Sorting Matrix Hash Function

#47

Rank

#1275MediumFrequency: 25.1%

Validate Binary Tree Nodes

Tree Depth-First Search Breadth-First Search Union-Find Graph Theory Binary Tree

#48

Rank

#1396MediumFrequency: 24.4%

Count Servers that Communicate

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

#49

Rank

#1840MediumFrequency: 24.4%

Minimize Hamming Distance After Swap Operations

Array Depth-First Search Union-Find

#50

Rank

#2213HardFrequency: 24.4%

Find All People With Secret

Depth-First Search Breadth-First Search Union-Find Graph Theory Sorting

#51

Rank

#2101HardFrequency: 23.3%

Last Day Where You Can Still Cross

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

#52

Rank

#989HardFrequency: 22.1%

Largest Component Size by Common Factor

Array Hash Table Math Union-Find Number Theory Prime Factorization

#53

Rank

#1257HardFrequency: 22.1%

Rank Transform of a Matrix

Array Union-Find Graph Theory Topological Sort Sorting Matrix

#54

Rank

#1815HardFrequency: 22.1%

Checking Existence of Edge Length Limited Paths

Array Two Pointers Union-Find Graph Theory Sorting

#55

Rank

#2505HardFrequency: 22.1%

Number of Good Paths

Array Hash Table Tree Union-Find Graph Theory Sorting

#56

Rank

#1144HardFrequency: 22%

Optimize Water Distribution in a Village

Asked at Apple

Union-Find Graph Theory Heap (Priority Queue)Minimum Spanning Tree Prim's Algorithm Kruskal's Algorithm Borůvka's Algorithm

#57

Rank

#737MediumFrequency: 22%

Sentence Similarity II

Asked at Apple

Array Hash Table String Depth-First Search Breadth-First Search Union-Find

#58

Rank

#685HardFrequency: 20.9%

Redundant Connection II

Depth-First Search Breadth-First Search Union-Find Graph Theory

#59

Rank

#964HardFrequency: 20.3%

Minimize Malware Spread II

Array Hash Table Depth-First Search Breadth-First Search Union-Find Graph Theory

#60

Rank

#2198HardFrequency: 20.3%

Process Restricted Friend Requests

Union-Find Graph Theory

#61

Rank

#3219MediumFrequency: 20.3%

Make Lexicographically Smallest Array by Swapping Elements

Array Union-Find Sorting

#62

Rank

#1100MediumFrequency: 20%

Connecting Cities With Minimum Cost

Union-Find Graph Theory Heap (Priority Queue)Minimum Spanning Tree

#63

Rank

#2995MediumFrequency: 20%

Number of Unique Categories

Union-Find Interactive Counting

#64

Rank

#821HardFrequency: 19.5%

Bricks Falling When Hit

Array Union-Find Matrix

#65

Rank

#2512MediumFrequency: 19.5%

Longest Uploaded Prefix

Hash Table Binary Search Union-Find Design Binary Indexed Tree Segment Tree Heap (Priority Queue)Ordered Set

#66

Rank

#770HardFrequency: 19.5%

Couples Holding Hands

Greedy Depth-First Search Breadth-First Search Union-Find Graph Theory

#67

Rank

#1692HardFrequency: 18%

Number of Ways to Reorder Array to Get Same BST

Array Math Divide and Conquer Dynamic Programming Tree Union-Find Binary Search Tree Memoization Combinatorics Binary Tree Fermat's Little Theorem

#68

Rank

#4010HardFrequency: 18%

Maximize Alternating Sum Using Swaps

Array Greedy Union-Find Sorting

#69

Rank

#1663MediumFrequency: 18%

Detect Cycles in 2D Grid

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

#70

Rank

#1058MediumFrequency: 18%

Lexicographically Smallest Equivalent String

String Union-Find

#71

Rank

#1865HardFrequency: 16.4%

Checking Existence of Edge Length Limited Paths II

Depth-First Search Union-Find Graph Theory Design Sorting Heap (Priority Queue)Minimum Spanning Tree

#72

Rank

#2506HardFrequency: 16.4%

Minimize Maximum Value in a Grid

Array Union-Find Graph Theory Topological Sort Sorting Matrix

#73

Rank

#3348HardFrequency: 16.4%

Minimum Cost Walk in Weighted Graph

Array Bit Manipulation Union-Find Graph Theory

#74

Rank

#2793MediumFrequency: 16.1%

Count the Number of Complete Components

Asked at Microsoft

Depth-First Search Breadth-First Search Union-Find Graph Theory

#75

Rank

#1032MediumFrequency: 14.6%

Satisfiability of Equality Equations

Array String Union-Find Graph Theory

#76

Rank

#2582MediumFrequency: 14.6%

Minimum Score of a Path Between Two Cities

Depth-First Search Breadth-First Search Union-Find Graph Theory

#77

Rank

#2764MediumFrequency: 12%

Maximum Number of Fish in a Grid

Asked at Microsoft

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

#78

Rank

#352HardFrequency: 8.1%

Data Stream as Disjoint Intervals

Hash Table Binary Search Union-Find Design Data Stream Ordered Set

#79

Rank

#2708HardFrequency: 8.1%

Find the String with LCP

Array String Dynamic Programming Greedy Union-Find Matrix

#80

Rank

#3902HardFrequency: 8.1%

Maximize Spanning Tree Stability with Upgrades

Binary Search Greedy Union-Find Graph Theory Minimum Spanning Tree

#81

Rank

#3823MediumFrequency: 5%

Count Islands With Total Value Divisible by K

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

#82

Rank

#2445MediumFrequency: 5%

Reachable Nodes With Restrictions

Array Hash Table Tree Depth-First Search Breadth-First Search Union-Find Graph Theory

#83

Rank

#4035HardFrequency: 5%

Maximum Partition Factor

Array Binary Search Depth-First Search Breadth-First Search Union-Find Graph Theory

#84

Rank

#1507MediumFrequency: 5%

Check if There is a Valid Path in a Grid

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

#85

Rank

#3478HardFrequency: 5%

Check if the Rectangle Corner Is Reachable

Array Math Depth-First Search Breadth-First Search Union-Find Geometry

#86

Rank

#3908MediumFrequency: 5%

Minimum Time for K Connected Components

Binary Search Union-Find Graph Theory Sorting

#87

Rank

#3809MediumFrequency: 5%

Properties Graph