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
1. Two Sum	Easy	57.8%	Array Hash Table	Read
2. Add Two Numbers	Medium	49.3%	Linked List Math+1	Read
3. Longest Substring Without Repeating Characters	Medium	39.9%	Hash Table Sliding Window+1	Read
4. Median of Two Sorted Arrays	Hard	47.3%	Array Binary Search+1	Read
5. Longest Palindromic Substring	Medium	38.7%	Dynamic Programming String+1	Read
6. Zigzag Conversion	Medium	54.9%	String	Read
7. Reverse Integer	Medium	32.2%	Math	Read
8. String to Integer (atoi)	Medium	21.4%	String	Read
9. Palindrome Number	Easy	61.0%	Math	Read
10. Regular Expression Matching	Hard	31.8%	Dynamic Programming Recursion+1	Read
11. Container With Most Water	Medium	60.9%	Array Greedy+1	Read
12. Integer to Roman	Medium	71.2%	Hash Table Math+1	Read
13. Roman to Integer	Easy	67.0%	Hash Table Math+1	Read
14. Longest Common Prefix	Easy	48.0%	String Trie	Read
15. 3Sum	Medium	39.5%	Array Sorting+1	Read
16. 3Sum Closest	Medium	47.4%	Array Sorting+1	Read
17. Letter Combinations of a Phone Number	Medium	66.9%	Backtracking Hash Table+1	Read
18. 4Sum	Medium	41.4%	Array Sorting+1	Read
19. Remove Nth Node From End of List	Medium	52.4%	Linked List Two Pointers	Read
20. Valid Parentheses	Easy	44.5%	Stack String	Read
21. Merge Two Sorted Lists	Easy	68.7%	Linked List Recursion	Read
22. Generate Parentheses	Medium	79.0%	Backtracking Dynamic Programming+1	Read
23. Merge k Sorted Lists	Hard	60.3%	Divide and Conquer Heap (Priority Queue)+2	Read
24. Swap Nodes in Pairs	Medium	70.3%	Linked List Recursion	Read
25. Reverse Nodes in k-Group	Hard	66.8%	Linked List Recursion	Read
26. Remove Duplicates from Sorted Array	Easy	63.7%	Array Two Pointers	Read
27. Remove Element	Easy	62.2%	Array Two Pointers	Read
28. Find the Index of the First Occurrence in a String	Easy	47.0%	String String Matching+1	Read
29. Divide Two Integers	Medium	20.1%	Bit Manipulation Math	Read
30. Substring with Concatenation of All Words	Hard	34.8%	Hash Table Sliding Window+1	Read
31. Next Permutation	Medium	46.1%	Array Two Pointers	Read
32. Longest Valid Parentheses	Hard	39.5%	Dynamic Programming Stack+1	Read
33. Search in Rotated Sorted Array	Medium	45.5%	Array Binary Search	Read
34. Find First and Last Position of Element in Sorted Array	Medium	49.7%	Array Binary Search	Read
35. Search Insert Position	Easy	52.1%	Array Binary Search	Read
36. Valid Sudoku	Medium	64.9%	Array Hash Table+1	Read
37. Sudoku Solver	Hard	65.4%	Array Backtracking+2	Read
38. Count and Say	Medium	63.7%	String	Read
39. Combination Sum	Medium	76.9%	Array Backtracking	Read
40. Combination Sum II	Medium	59.7%	Array Backtracking	Read
41. First Missing Positive	Hard	43.8%	Array Hash Table	Read
42. Trapping Rain Water	Hard	68.2%	Array Dynamic Programming+3	Read
43. Multiply Strings	Medium	44.4%	Math Simulation+1	Read
44. Wildcard Matching	Hard	32.8%	Dynamic Programming Greedy+2	Read
45. Jump Game II	Medium	43.2%	Array Dynamic Programming+1	Read
46. Permutations	Medium	82.3%	Array Backtracking	Read
47. Permutations II	Medium	63.7%	Array Backtracking	Read
48. Rotate Image	Medium	80.7%	Array Math+1	Read
49. Group Anagrams	Medium	73.0%	Array Hash Table+2	Read
50. Pow(x, n)	Medium	39.0%	Math Recursion	Read

#1Easy

Two Sum

ArrayHash Table

Acceptance: 57.8%

#2Medium

Add Two Numbers

Linked ListMathRecursion

Acceptance: 49.3%

#3Medium

Longest Substring Without Repeating Characters

Hash TableSliding WindowString

Acceptance: 39.9%

#4Hard

Median of Two Sorted Arrays

ArrayBinary SearchDivide and Conquer

Acceptance: 47.3%

#5Medium

Longest Palindromic Substring

Dynamic ProgrammingStringTwo Pointers

Acceptance: 38.7%

#6Medium

Zigzag Conversion

String

Acceptance: 54.9%

#7Medium

Reverse Integer

Math

Acceptance: 32.2%

#8Medium

String to Integer (atoi)

String

Acceptance: 21.4%

#9Easy

Palindrome Number

Math

Acceptance: 61.0%

#10Hard

Regular Expression Matching

Dynamic ProgrammingRecursionString

Acceptance: 31.8%

#11Medium

Container With Most Water

ArrayGreedyTwo Pointers

Acceptance: 60.9%

#12Medium

Integer to Roman

Hash TableMathString

Acceptance: 71.2%

#13Easy

Roman to Integer

Hash TableMathString

Acceptance: 67.0%

#14Easy

Longest Common Prefix

StringTrie

Acceptance: 48.0%

#15Medium

3Sum

ArraySortingTwo Pointers

Acceptance: 39.5%

#16Medium

3Sum Closest

ArraySortingTwo Pointers

Acceptance: 47.4%

#17Medium

Letter Combinations of a Phone Number

BacktrackingHash TableString

Acceptance: 66.9%

#18Medium

4Sum

ArraySortingTwo Pointers

Acceptance: 41.4%

#19Medium

Remove Nth Node From End of List

Linked ListTwo Pointers

Acceptance: 52.4%

#20Easy

Valid Parentheses

StackString

Acceptance: 44.5%

#21Easy

Merge Two Sorted Lists

Linked ListRecursion

Acceptance: 68.7%

#22Medium

Generate Parentheses

BacktrackingDynamic ProgrammingString

Acceptance: 79.0%

#23Hard

Merge k Sorted Lists

Divide and ConquerHeap (Priority Queue)Linked List+1

Acceptance: 60.3%

#24Medium

Swap Nodes in Pairs

Linked ListRecursion

Acceptance: 70.3%

#25Hard

Reverse Nodes in k-Group

Linked ListRecursion

Acceptance: 66.8%

#26Easy

Remove Duplicates from Sorted Array

ArrayTwo Pointers

Acceptance: 63.7%

#27Easy

Remove Element

ArrayTwo Pointers

Acceptance: 62.2%

#28Easy

Find the Index of the First Occurrence in a String

StringString MatchingTwo Pointers

Acceptance: 47.0%

#29Medium

Divide Two Integers

Bit ManipulationMath

Acceptance: 20.1%

#30Hard

Substring with Concatenation of All Words

Hash TableSliding WindowString

Acceptance: 34.8%

#31Medium

Next Permutation

ArrayTwo Pointers

Acceptance: 46.1%

#32Hard

Longest Valid Parentheses

Dynamic ProgrammingStackString

Acceptance: 39.5%

#33Medium

Search in Rotated Sorted Array

ArrayBinary Search

Acceptance: 45.5%

#34Medium

Find First and Last Position of Element in Sorted Array

ArrayBinary Search

Acceptance: 49.7%

#35Easy

Search Insert Position

ArrayBinary Search

Acceptance: 52.1%

#36Medium

Valid Sudoku

ArrayHash TableMatrix

Acceptance: 64.9%

#37Hard

Sudoku Solver

ArrayBacktrackingHash Table+1

Acceptance: 65.4%

#38Medium

Count and Say

String

Acceptance: 63.7%

#39Medium

Combination Sum

ArrayBacktracking

Acceptance: 76.9%

#40Medium

Combination Sum II

ArrayBacktracking

Acceptance: 59.7%

#41Hard

First Missing Positive

ArrayHash Table

Acceptance: 43.8%

#42Hard

Trapping Rain Water

ArrayDynamic ProgrammingMonotonic Stack+2

Acceptance: 68.2%

#43Medium

Multiply Strings

MathSimulationString

Acceptance: 44.4%

#44Hard

Wildcard Matching

Dynamic ProgrammingGreedyRecursion+1

Acceptance: 32.8%

#45Medium

Jump Game II

ArrayDynamic ProgrammingGreedy

Acceptance: 43.2%

#46Medium

Permutations

ArrayBacktracking

Acceptance: 82.3%

#47Medium

Permutations II

ArrayBacktracking

Acceptance: 63.7%

#48Medium

Rotate Image

ArrayMathMatrix

Acceptance: 80.7%

#49Medium

Group Anagrams

ArrayHash TableSorting+1

Acceptance: 73.0%

#50Medium

Pow(x, n)

MathRecursion

Acceptance: 39.0%

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