Solutions & Explanations

Browse 4,029+ detailed solutions with multiple approaches, code in Python, Java, C++ and more.

4,029 Solutions961 Easy2102 Medium966 Hard

Title	Difficulty	Acceptance	Topics	Solution
614. Second Degree Follower	Medium	39.3%	Database	Read
616. Add Bold Tag in String	Medium	51.4%	Array Hash Table+3	Read
621. Task Scheduler	Medium	63.4%	Array Counting+4	Read
622. Design Circular Queue	Medium	55.4%	Array Design+2	Read
623. Add One Row to Tree	Medium	64.1%	Binary Tree Breadth-First Search+2	Read
624. Maximum Distance in Arrays	Medium	45.7%	Array Greedy	Read
625. Minimum Factorization	Medium	34.2%	Greedy Math	Read
626. Exchange Seats	Medium	71.6%	Database	Read
633. Sum of Square Numbers	Medium	37.0%	Binary Search Math+1	Read
634. Find the Derangement of An Array	Medium	41.9%	Dynamic Programming Math	Read
635. Design Log Storage System	Medium	59.8%	Design Hash Table+2	Read
636. Exclusive Time of Functions	Medium	66.2%	Array Stack	Read
638. Shopping Offers	Medium	52.3%	Array Backtracking+4	Read
640. Solve the Equation	Medium	46.7%	Math Simulation+1	Read
641. Design Circular Deque	Medium	64.6%	Array Design+2	Read
646. Maximum Length of Pair Chain	Medium	62.2%	Array Dynamic Programming+2	Read
647. Palindromic Substrings	Medium	73.2%	Dynamic Programming String+1	Read
648. Replace Words	Medium	68.7%	Array Hash Table+2	Read
649. Dota2 Senate	Medium	50.3%	Greedy Queue+1	Read
650. 2 Keys Keyboard	Medium	59.6%	Dynamic Programming Math	Read
651. 4 Keys Keyboard	Medium	56.5%	Dynamic Programming Math	Read
652. Find Duplicate Subtrees	Medium	60.6%	Binary Tree Depth-First Search+2	Read
654. Maximum Binary Tree	Medium	86.3%	Array Binary Tree+4	Read
655. Print Binary Tree	Medium	66.5%	Binary Tree Breadth-First Search+2	Read
658. Find K Closest Elements	Medium	50.1%	Array Binary Search+4	Read
659. Split Array into Consecutive Subsequences	Medium	52.1%	Array Greedy+2	Read
662. Maximum Width of Binary Tree	Medium	46.0%	Binary Tree Breadth-First Search+2	Read
663. Equal Tree Partition	Medium	42.3%	Binary Tree Depth-First Search+1	Read
665. Non-decreasing Array	Medium	25.5%	Array	Read
666. Path Sum IV	Medium	62.5%	Array Binary Tree+3	Read
667. Beautiful Arrangement II	Medium	61.1%	Array Math	Read
669. Trim a Binary Search Tree	Medium	66.9%	Binary Search Tree Binary Tree+2	Read
670. Maximum Swap	Medium	51.6%	Greedy Math	Read
672. Bulb Switcher II	Medium	50.6%	Bit Manipulation Breadth-First Search+2	Read
673. Number of Longest Increasing Subsequence	Medium	52.8%	Array Binary Indexed Tree+2	Read
676. Implement Magic Dictionary	Medium	57.8%	Depth-First Search Design+3	Read
677. Map Sum Pairs	Medium	57.4%	Design Hash Table+2	Read
678. Valid Parenthesis String	Medium	40.5%	Dynamic Programming Greedy+2	Read
681. Next Closest Time	Medium	46.8%	Backtracking Enumeration+2	Read
684. Redundant Connection	Medium	68.0%	Breadth-First Search Depth-First Search+2	Read
686. Repeated String Match	Medium	39.7%	String String Matching	Read
687. Longest Univalue Path	Medium	44.3%	Binary Tree Depth-First Search+1	Read
688. Knight Probability in Chessboard	Medium	57.0%	Dynamic Programming	Read
690. Employee Importance	Medium	69.4%	Array Breadth-First Search+3	Read
692. Top K Frequent Words	Medium	60.6%	Bucket Sort Counting+5	Read
694. Number of Distinct Islands	Medium	62.8%	Breadth-First Search Depth-First Search+3	Read
695. Max Area of Island	Medium	73.9%	Array Breadth-First Search+3	Read
698. Partition to K Equal Sum Subsets	Medium	38.6%	Array Backtracking+4	Read
701. Insert into a Binary Search Tree	Medium	73.6%	Binary Search Tree Binary Tree+1	Read
702. Search in a Sorted Array of Unknown Size	Medium	73.1%	Array Binary Search+1	Read

#614Medium

Second Degree Follower

Database

Acceptance: 39.3%

#616Medium

Add Bold Tag in String

ArrayHash TableString+2

Acceptance: 51.4%

#621Medium

Task Scheduler

ArrayCountingGreedy+3

Acceptance: 63.4%

#622Medium

Design Circular Queue

ArrayDesignLinked List+1

Acceptance: 55.4%

#623Medium

Add One Row to Tree

Binary TreeBreadth-First SearchDepth-First Search+1

Acceptance: 64.1%

#624Medium

Maximum Distance in Arrays

ArrayGreedy

Acceptance: 45.7%

#625Medium

Minimum Factorization

GreedyMath

Acceptance: 34.2%

#626Medium

Exchange Seats

Database

Acceptance: 71.6%

#633Medium

Sum of Square Numbers

Binary SearchMathTwo Pointers

Acceptance: 37.0%

#634Medium

Find the Derangement of An Array

Dynamic ProgrammingMath

Acceptance: 41.9%

#635Medium

Design Log Storage System

DesignHash TableOrdered Set+1

Acceptance: 59.8%

#636Medium

Exclusive Time of Functions

ArrayStack

Acceptance: 66.2%

#638Medium

Shopping Offers

ArrayBacktrackingBit Manipulation+3

Acceptance: 52.3%

#640Medium

Solve the Equation

MathSimulationString

Acceptance: 46.7%

#641Medium

Design Circular Deque

ArrayDesignLinked List+1

Acceptance: 64.6%

#646Medium

Maximum Length of Pair Chain

ArrayDynamic ProgrammingGreedy+1

Acceptance: 62.2%

#647Medium

Palindromic Substrings

Dynamic ProgrammingStringTwo Pointers

Acceptance: 73.2%

#648Medium

Replace Words

ArrayHash TableString+1

Acceptance: 68.7%

#649Medium

Dota2 Senate

GreedyQueueString

Acceptance: 50.3%

#650Medium

2 Keys Keyboard

Dynamic ProgrammingMath

Acceptance: 59.6%

#651Medium

4 Keys Keyboard

Dynamic ProgrammingMath

Acceptance: 56.5%

#652Medium

Find Duplicate Subtrees

Binary TreeDepth-First SearchHash Table+1

Acceptance: 60.6%

#654Medium

Maximum Binary Tree

ArrayBinary TreeDivide and Conquer+3

Acceptance: 86.3%

#655Medium

Print Binary Tree

Binary TreeBreadth-First SearchDepth-First Search+1

Acceptance: 66.5%

#658Medium

Find K Closest Elements

ArrayBinary SearchHeap (Priority Queue)+3

Acceptance: 50.1%

#659Medium

Split Array into Consecutive Subsequences

ArrayGreedyHash Table+1

Acceptance: 52.1%

#662Medium

Maximum Width of Binary Tree

Binary TreeBreadth-First SearchDepth-First Search+1

Acceptance: 46.0%

#663Medium

Equal Tree Partition

Binary TreeDepth-First SearchTree

Acceptance: 42.3%

#665Medium

Non-decreasing Array

Array

Acceptance: 25.5%

#666Medium

Path Sum IV

ArrayBinary TreeDepth-First Search+2

Acceptance: 62.5%

#667Medium

Beautiful Arrangement II

ArrayMath

Acceptance: 61.1%

#669Medium

Trim a Binary Search Tree

Binary Search TreeBinary TreeDepth-First Search+1

Acceptance: 66.9%

#670Medium

Maximum Swap

GreedyMath

Acceptance: 51.6%

#672Medium

Bulb Switcher II

Bit ManipulationBreadth-First SearchDepth-First Search+1

Acceptance: 50.6%

#673Medium

Number of Longest Increasing Subsequence

ArrayBinary Indexed TreeDynamic Programming+1

Acceptance: 52.8%

#676Medium

Implement Magic Dictionary

Depth-First SearchDesignHash Table+2

Acceptance: 57.8%

#677Medium

Map Sum Pairs

DesignHash TableString+1

Acceptance: 57.4%

#678Medium

Valid Parenthesis String

Dynamic ProgrammingGreedyStack+1

Acceptance: 40.5%

#681Medium

Next Closest Time

BacktrackingEnumerationHash Table+1

Acceptance: 46.8%

#684Medium

Redundant Connection

Breadth-First SearchDepth-First SearchGraph+1

Acceptance: 68.0%

#686Medium

Repeated String Match

StringString Matching

Acceptance: 39.7%

#687Medium

Longest Univalue Path

Binary TreeDepth-First SearchTree

Acceptance: 44.3%

#688Medium

Knight Probability in Chessboard

Dynamic Programming

Acceptance: 57.0%

#690Medium

Employee Importance

ArrayBreadth-First SearchDepth-First Search+2

Acceptance: 69.4%

#692Medium

Top K Frequent Words

Bucket SortCountingHash Table+4

Acceptance: 60.6%

#694Medium

Number of Distinct Islands

Breadth-First SearchDepth-First SearchHash Function+2

Acceptance: 62.8%

#695Medium

Max Area of Island

ArrayBreadth-First SearchDepth-First Search+2

Acceptance: 73.9%

#698Medium

Partition to K Equal Sum Subsets

ArrayBacktrackingBit Manipulation+3

Acceptance: 38.6%

#701Medium

Insert into a Binary Search Tree

Binary Search TreeBinary TreeTree

Acceptance: 73.6%

#702Medium

Search in a Sorted Array of Unknown Size

ArrayBinary SearchInteractive

Acceptance: 73.1%

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Master DSA with Step-by-Step Solutions

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How to Use These Solutions

Try the problem first: Spend at least 20 minutes before reading the solution
Read all approaches: Start from brute force to understand the problem fully, then study the optimized solution
Understand the complexity: Pay attention to time and space analysis for each approach
Code it yourself: After understanding the approach, close the solution and implement from memory
Revisit after a week: Spaced repetition helps retain problem-solving patterns