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LeetCode 2. Add Two NumbersDescriptionExampleCodeConclusionDescriptionYou are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each...

LeetCode 24. Swap Nodes in PairsDescriptionExampleCodeConclusionDescriptionGiven a linked list, swap every two adjacent nodes and return its head.You may not modify the values in the list’s nodes, ...

LeetCode 25. Reverse Nodes in k-GroupDescriptionExampleNoteCodeConclusionDescriptionGiven a linked list, reverse the nodes of a linked list k at a time and return its modified list.k is a positive ...

LeetCode 26. Remove Duplicates from Sorted ArrayDescriptionExampleClarificationCodeConclusionDescriptionGiven a sorted array nums, remove the duplicates in-place such that each element appear only o...

LeetCode 17. Letter Combinations of a Phone NumberDescriptionExampleNoteCodeConclusionDescriptionGiven a string containing digits from 2-9 inclusive, return all possible letter combinations that the...

LeetCode 27. Remove ElementDescriptionExampleClarificationCodeConclusionDescriptionGiven an array nums and a value val, remove all instances of that value in-place and return the new length.Do not ...

LeetCode 22. Generate ParenthesesDescriptionExampleCodeConclusionDescriptionGiven n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.ExampleFor exampl...

LeetCode 23. Merge k Sorted ListsDescriptionExampleCodeConclusionDescriptionMerge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.ExampleInput:[ 1-&g...

LeetCode 30. Substring with Concatenation of All WordsDescriptionExampleCodeConclusionDescriptionYou are given a string, s, and a list of words, words, that are all of the same length. Find all star...

LeetCode 28. Implement strStrDescriptionExampleClarificationCodeConclusionDescriptionImplement strStr().Return the index of the first occurrence of needle in haystack, or -1 if needle is not part o...

LeetCode 29. Divide Two IntegersDescriptionExampleNoteCodeConclusionDescriptionGiven two integers dividend and divisor, divide two integers without using multiplication, division and mod operator.R...

LeetCode 50. Pow(x, nDescriptionExampleNoteCodeConclusionDescriptionImplement pow(x, n), which calculates x raised to the power n (xn).ExampleNote-100.0 < x < 100.0n is a 32-bit signed i...

LeetCode 39. Combination SumDescriptionNoteExampleCodeConclusionDescriptionGiven a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinatio...

LeetCode 40. Combination Sum IIDescriptionNoteExampleCodeConclusionDescriptionGiven a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candi...

LeetCode 41. First Missing PositiveDescriptionNoteExampleCodeConclusionDescriptionGiven an unsorted integer array, find the smallest missing positive integer.NoteYour algorithm should run in O(n) ...

LeetCode 16. 3Sum ClosestDescriptionExampleCodeConclusionDescriptionGiven an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Retur...

LeetCode 21. Merge Two Sorted ListsDescriptionExampleCodeConclusionDescriptionMerge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of...

LeetCode 15. 3SumDescriptionExampleCodeConclusionDescriptionGiven an array numsof n integers, are there elements a, b, c in numssuch that a + b + c = 0? Find all unique triplets in the array which g...

LeetCode 3. Longest Substring Without Repeating CharactersDescriptionExampleCodeConclusionDescriptionGiven a string, find the length of the longest substring without repeating characters.ExampleC...

LeetCode 4. Median of Two Sorted ArraysDescriptionExampleCodeConclusionDescriptionThere are two sorted arrays nums1 and nums2 of size m and n respectively.Find the median of the two sorted arrays. ...

LeetCode 7. Reverse IntegerDescriptionExampleCodeConclusionDescriptionGiven a 32-bit signed integer, reverse digits of an integer.ExampleCodejavaclass Solution { public int reverse(int x)...

LeetCode 11. Container With Most WaterDescriptionExampleCodeConclusionDescriptionGiven n non-negative integers a1, a2, …, an , where each represents a point at coordinate (i, ai). n vertical lines a...

LeetCode 6. ZigZag ConversionDescriptionExampleCodeConclusionDescriptionExampleCodejavaclass Solution { public String convert(String s, int numRows) { if(numRows < 2 || s == nu...

LeetCode 8. String to Integer (atoiDescriptionNoteExampleCodeConclusionDescriptionImplement atoi which converts a string to an integer.The function first discards as many whitespace characters as n...

LeetCode 12. Integer to RomanDescriptionExampleCodeConclusionDescriptionRoman numerals are represented by seven different symbols: I, V, X, L, C, D and M.Symbol ValueI 1V ...

LeetCode 9. Palindrome NumberDescriptionExampleFollow upCodeConclusionDescriptionDetermine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward....

LeetCode 13. Roman to IntegerDescriptionExampleCodeConclusionDescriptionRoman numerals are represented by seven different symbols: I, V, X, L, C, D and M.Symbol ValueI 1V ...

LeetCode 10. Regular Expression MatchingDescriptionNoteExampleCodeConclusionDescriptionGiven an input string (s) and a pattern (p), implement regular expression matching with support for'.'and'*'....

LeetCode 18. 4SumDescriptionExampleNoteCodeConclusionDescriptionGiven an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? F...

LeetCode 19. Remove Nth Node From End of ListDescriptionExampleNoteCodeConclusionDescriptionGiven a linked list, remove the n-th node from the end of list and return its head.ExampleNoteGiven n ...

LeetCode 14. Longest Common PrefixDescriptionExampleNoteCodeConclusionDescriptionWrite a function to find the longest common prefix string amongst an array of strings.If there is no common prefix, ...

LeetCode 20. Valid ParenthesesDescriptionExampleCodeConclusionDescriptionGiven a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.An inp...

LeetCode 47. Permutations IIDescriptionExampleCodeConclusionDescriptionGiven a collection of numbers that might contain duplicates, return all possible unique permutations.ExampleCodejavaclas...