By Long Luo
我的 Leetcode 的解题：
Chinese SolutionsLeetcode题目难度题解1. 两数之和Easy2种方法：暴力 和 HashMap2. 两数相加Medium2种方法：模拟 和 递归4. 寻找两个正序数组的中位数Hard4种方法：合并数组，暴力法，二分搜索，划分数组15. 三数之和Medium3种方法：暴力，Hash，双指针18. 四数之和Medium4种方法：暴力，双指针，DFS，HashMap22. 括号生成Medium2种方法：暴力法 和 回溯法28. 实现 strStr()Easy理解KMP算法：从入门到推导29. 两数相除Medium3种方法：暴力法，二分搜索，递归42. 接雨水Hard5种解法：木桶原理，按行求，动态规划，双指针，单调栈43. 字符串相乘Medium另辟蹊径，快速傅里叶变换(FFT)计算大数乘法70. 爬楼梯Easy面试算法题：爬楼梯，N级楼梯有多少种走法？148. 排序链表Medium4种方法：暴力，List，自顶向下归并排序，自底向上归并排序155. 最小栈Easy3种方法：辅助栈，栈，链表171. Excel 表列序号Easy仿照Excel的列编号，给定一个数字，输出该列编号字符串209. 长度最小的子数组Medium5种方法：暴力，双指针，前缀和，前缀和 + 二分查找，二分查找225. 用队列实现栈Easy如何改变队列元素顺序？230. 二叉搜索树中第K小的元素Medium二叉搜索树中第K小的元素232. 用栈实现队列Easy顺序翻转，使用两个栈：一个入队，一个出队268. 丢失的数字Medium4种方法：排序，哈希表，异或，数学公式299. 猜数字游戏Medium从遍历2次优化到遍历1次318. 最大单词长度乘积Medium3种方法：从暴力状态压缩到位运算优化384. 打乱数组Medium2种方法：暴力 和 洗牌算法390. 消除游戏Medium经典算法：从约瑟夫问题说开去…396. 旋转函数Medium3种方法：暴力法，动态规划，前缀和 + 滑动窗口407. 接雨水 IIHard2种方法：优先队列存储每层围栏最低高度，BFS更新每个方块存水高度超大数字的加减乘除 415. 字符串相加, 445. 两数相加 IIMedium超大数字的四则运算是如何实现的呢？419. 甲板上的战舰Medium4种方法：一次遍历，DFS，统计战舰起点423. 从英文中重建数字Medium找规律，依次确定数字的次数，逐步消元法438. 找到字符串中所有字母异位词Medium滑动窗口：从HashMap，数组，再到统计字母数量之差458. 可怜的小猪Hard从 经典面试问题 到 信息论509. 斐波那契数Easy9种求斐波那契数(Fibonacci Numbers)的算法519. 随机翻转矩阵Medium2种方法：暴力法 和 降维 + 哈希表525. 连续数组Medium2种方法：暴力，前缀和 + 哈希表559. N叉树的最大深度Easy3种方法：递归，DFS和BFS594. 最长和谐子序列Easy4种方法：暴力枚举，排序 + 枚举，哈希表598. 范围求和 IIEasy求所有操作的交集686. 重复叠加字符串匹配Medium3种方法：暴力，字符串哈希，KMP700. 二叉搜索树中的搜索Easy3种方法：递归，迭代，BFS859. 亲密字符串Easy简单的字符串模拟912. 排序数组Medium排序算法(Sorting Algorithms)997. 找到小镇的法官Easy图论，计算各节点的入度和出度1044. 最长重复子串Hard3种方法：从暴力到二分，二分搜索 + 字符串哈希，后缀数组1218. 最长定差子序列Medium序列动态规划 + HashMap1385. 两个数组间的距离值Easy2种方法：模拟 和 二分搜索1705. 吃苹果的最大数目Medium贪心 + 优先队列：每天找最邻近过期的苹果吃1816. 截断句子Easy3种方法：正则表达式，模拟和优化meituan-002. 小美的仓库整理Medium记一道美团面试编程题的解题过程：从暴力到优化English Solutions on My WebsiteSolutions on My Website.
Leetcode ProblemsDifficultySolutions2. Add Two NumbersEasyJava Linkedlist Iteration and Recusion Solution11. Container With Most WaterMedium2 Approaches: BF and Two Pointers with Image Explaination and Code Commented17. Letter Combinations of a Phone NumberMedium4 Approaches: BF 4 Loops, Backtracking, BFS, Queue with Image Explaination31. Next PermutationMediumTwo Pointers Solution with Detailed Explanation and Code Commented34. Find First and Last Position of Element in Sorted ArrayMediumBinary Search Twice36. Valid SudokuMedium2 Solutions Using HashSet + Array39. Combination SumMediumThe Key of the Backtrack is Deduplicating and Pruning50. Pow(x, n)MediumIllustration of Fast Power Algorithm - Exponentiation by Squaring or Binary Exponentiation62. Unique PathsMedium3 Approaches: Dynamic Programming, Recursion, Math69. Sqrt(x)Medium4 Approaches for Finding the Square Root of A Number: BF, Exponent, Binary Search and Newton Iteration Method70. Climbing StairsEasy9 Fibonacci Algorithms: the Most Complete Solutions All In One71. Simplify PathMediumjava/python/go Using Stack with Easy Detailed Explanations74. Search a 2D MatrixMedium6 Approaches BF + 2D Coords + 2 Binary Search + 1 Binary Search + Row Scan114. Flatten Binary Tree to Linked ListMediumRecursive Solution with 3-steps and Image Explanation117. Populating Next Right Pointers in Each Node IIMedium3 Approaches: BFS, BFS + LinkedList, Recursion120. TriangleMediumDP: Top-Down and Bottom-Up Approach136. Single NumberEasy5 Lines Code / The XOR operator Cheatsheet / Bitwise Operation / with Easy Detailed ExplanationBinary and N-ary Tree Traversal: 144. Binary Tree Preorder TraversalEasyTree Traversals All In One: PreOrder, InOrder and PostOrder167. Two Sum II - Input Array Is SortedMedium4 Approaches: Brute Force, HashMap, Binary Search, Two Pointers171. Excel Sheet Column NumberEasyBase Conversion 2 Solutions: Left to Right and Right to Left215. Kth Largest Element in an ArrayMedium3 Approaches: Sorting, Priority Queue, Divide and Conquer216. Combination Sum IIIMedium2 Approaches: Backtracking and Bit Mask219. Contains Duplicate IIEasy3 Solutions with Brute Force, HashMap and Sliding Window240. Search a 2D Matrix IIMedium5 Approaches: BF, Binary Search(Row), Binary Search(Diagonal, Row, Col), Binary Search(Global), 2D Coord Axis242. Valid AnagramEasy3 Solutions: HashMap, Sort and Count Count is the Fastest287. Find the Duplicate NumberMedium9 Approaches: Count, Hash, Sort, Binary Search, Bit, Fast Slow Pointers300. Longest Increasing SubsequenceMedium3 Approaches: Backtrack, DP, Binary Search316. Remove Duplicate LettersMediumThe Detailed Explanation with 3-steps to Understand the Stack Solution Easy329. Longest Increasing Path in a MatrixHard4 Approaches: BFS, Memory + DFS, DP, Topological Sorting341. Flatten Nested List IteratorMedium2 Approaches: DFS, Iteration(Using Stack)344. Reverse StringEasy2 Approaches: Two Pointers and Recursion350. Intersection of Two Arrays IIEasy2 Solutions: Sort with Two Pointers and HashMap372. Super PowMediumJava Fast Power Algorithm377. Combination Sum IVMedium2 Approaches: Backtrack and DP with Follow Up Analysis378. Kth Smallest Element in a Sorted MatrixMedium3 Approaches: Sorting, Merge Sort, Binary Search399. Evaluate DivisionMedium4 Approaches: BFS, DFS, Floyd, Union Find406. Queue Reconstruction by HeightMediumPattern of Data Pairs Problem: Sorting First then Greedy440. K-th Smallest in Lexicographical OrderMedium456. 132 PatternMedium6 Approaches: BF O(n^3), BF O(n^2), TreeMap, Monotonic Stack509. Fibonacci NumberEasy9 Fibonacci Algorithms: the Most Complete Solutions All In One617. Merge Two Binary TreesEasy4 Approaches: Recursion, BFS and DFS763. Partition Labels)MediumIllustration of the Max Position of the Char in the Partition with Easy Detailed Explanation856. Score of ParenthesesMedium5 Solutions from Beginner to Expert with Stack to O(1) Space Detailed Explanation858. Mirror ReflectionMediumWhat If the Ray Not Reflected and Expand the Room with Image Explanation881. Boats to Save PeopleMediumGreedy: Let the Heaviest match the lightest, if not matched, let it alone895. Maximum Frequency StackHardThe Detailed Explanation using 2-Steps to Understand the HashMap + LinkedList Solution991. Broken CalculatorMediumGreedy: Reverse Thinking with Binary Algorithm946. Validate Stack SequencesMedium4 Solutions Using Array and Stack with Easy Detailed Explanation1091. Shortest Path in Binary MatrixMediumWhy Use BFS? Search Every Possible Path vs Search A Possible Path1249. Minimum Remove to Make Valid ParenthesesMediumUsing Stack with Easy Detailed Explanation of 2-steps Algorithm1631. Path With Minimum EffortMedium3 Approaches: BFS(Dijkstra), Binary Search, Union Find1642. Furthest Building You Can ReachMediumPriority Queue + Greedy: Consider Ladder as a One-time Unlimited Bricks1721. Swapping Nodes in a Linked ListMedium3 Approaches: Swapping Values and Swapping Nodes with Image Explaination and Code Commented1780. Check if Number is a Sum of Powers of ThreeEasy3 Solutions: Tricky, Recursive and Base 3 convertion1834. Single-Threaded CPUMediumHow to Maintain the Enqueued Tasks? Sorting the array then Priority QueueEnglish Solutions on LeetCodeSolutions on Leetcode.
All code are in Github.
Leetcode ProblemsDifficultySolutions2. Add Two NumbersEasy2 Approaches: Iteration and Recursion3. Longest Substring Without Repeating CharactersEasyTwo Pointers: Sliding Window with HashSet11. Container With Most WaterMedium2 Approaches: Brute Force and Two Pointers with Image Explanation17. Letter Combinations of a Phone NumberMedium4 Approaches: BF 4 Loops, Backtracking, BFS, Queue with Image Explaination19. Remove Nth Node From End of ListMedium3 Approaches: Brute Force, Stack, Slow Fast Pointers with Animation21. Merge Two Sorted ListsEasyThe Recursive Algorithm with Detailed Image Explanation29. Divide Two IntegersMedium5 Approaches: BF use Long, BF use Int, Binary Search use Long, Binary Search use Int and Recursion31. Next PermutationMediumTwo Pointers Solution with Detailed Explanation and Code Commented34. Find First and Last Position of Element in Sorted ArrayMediumBinary Search Twice36. Valid SudokuMedium2 Approaches: HashSet and Array39. Combination SumMediumEasy Backtracking Approach: Deduplicating and Pruning42. Trapping Rain WaterHardFrom Brute Force to DP then Two Pointers with Detail Explaination43. Multiply StringsMediumMath Geek: Fast Fourier Transform and Number Theoretic Transform47. Permutations IIMediumPermutation Problems: Backtracking and Pruning50. Pow(x, n)MediumFast Power Algorithm: Binary Exponentiation55. Jump GameMediumLeetcode Jump Game Problems Series62. Unique PathsMedium3 Approaches: DP, Recursion, Math69. Sqrt(x)Medium4 Approaches: Brute Force, Exponent, Binary Search and the Newton Iteration Method70. Climbing StairsEasy9 Fibonacci Algorithms: the Most Complete Solutions All In One71. Simplify PathMediumStack Solution with Easy Detailed Explanation74. Search a 2D MatrixMedium6 Approaches: Brute Force, Row Search, Column Search, One Binary Search, 2D Coordinate Axis81. Search in Rotated Sorted Array IIMediumBinary Search: The Key is Narrow the Search Interval Step by Step88. Merge Sorted ArrayEasy3 Approaches: Sorting, Two Pointers and Reverse Two Pointers98. Validate Binary Search TreeMedium3 Approaches: Recursion, DFS and Iteration102. Binary Tree Level Order TraversalMediumJava Simple BFS Solution114. Flatten Binary Tree to Linked ListMediumImage Explanation to Understand the Recursion Solution117. Populating Next Right Pointers in Each Node IIMedium3 Approaches: BFS, BFS + LinkedList, Recursion118. Pascal’s TriangleEasyMath Intuition of Dynamic Programming: Shift One and Added120. TriangleMediumDynamic Programming Space O(n) Solutions: Top-Down and Bottom-Up Approaches125. Valid PalindromeEasySimple Two Pointers Solution136. Single NumberEasyThe XOR Cheat Sheet and Bit Manipulation with Easy Detailed ExplanationBinary and N-ary Tree Traversal: 144. Binary Tree Preorder TraversalEasyTree Traversals All In One: PreOrder, InOrder and PostOrder160. Intersection of Two Linked ListsEasy2 Approaches: HashSet and Two Pointers with Detailed Explanation167. Two Sum II - Input Array Is SortedMedium4 Approaches: Brute Force, HashMap, Binary Search, Two Pointers171. Excel Sheet Column NumberEasy2 Approaches: Base Conversion from High to Low and from Low to High191. Number of 1 BitsEasy6 Approaches: Cycle, API, Divide and Conquer, Low Bit, Bit Set, Recursion199. Binary Tree Right Side ViewMedium2 Approaches: DFS and BFS with Detailed Explanation215. Kth Largest Element in an ArrayMedium3 Approaches: Sorting, Priority Queue, Divide and Conquer216. Combination Sum IIIMedium2 Approaches: Backtracking and Bit Mask219. Contains Duplicate IIEasy3 Approaches: Brute Force, HashMap and Sliding Window240. Search a 2D Matrix IIMedium5 Approaches: Brute Force, Binary Search(Row), Binary Search(Diagonal, Row, Col), Binary Search(Global), 2D Coord Axis242. Valid AnagramEasy3 Approaches: HashMap, Sorting and Counting268. Missing NumberEasy4 Approaches: Sorting, Hash, XOR, Math278. First Bad VersionEasyJava Binary Search Solution287. Find the Duplicate NumberMedium9 Approaches：Brute Force, Count, Hash, In-place Marked, Sorting, Index Sort, Binary Search, Bit Manipulation, Fast Slow Pointers295. Find Median from Data StreamMediumTwo Heaps with the Follow Up’s Solution300. Longest Increasing SubsequenceMedium3 Approaches: Backtrack, DP, Binary Search316. Remove Duplicate LettersMediumThe Detailed Explanation with 3-Steps to Understand the Stack Approach322. Coin ChangeMedium3 Approaches: DFS, BFS, DP329. Longest Increasing Path in a MatrixHard4 Approaches: BFS, Memory + DFS, DP, Topological Sorting334. Increasing Triplet SubsequenceMediumWhy Greedy works?341. Flatten Nested List IteratorMedium2 Approaches: DFS and Iteration(Using Stack)342. Power of FourEasyJust One Line Code and Detailed Explanation344. Reverse StringEasy2 Approaches: Two Pointers and Recursion350. Intersection of Two Arrays IIEasy2 Approaches: Sorting with Two Pointers and HashMap372. Super PowMedium2 Approaches: Brute Force and Binary Exponentiation377. Combination Sum IVMedium2 Approaches: Backtrack and DP with Follow Up Analysis378. Kth Smallest Element in a Sorted MatrixMedium3 Approaches: Sorting, Merge Sort, Binary Search399. Evaluate DivisionMedium4 Approaches: BFS, DFS, Floyd, Union Find406. Queue Reconstruction by HeightMediumPattern of Data Pairs Problem: Sorting First then Greedy429. N-ary Tree Level Order TraversalMediumTraverse the Tree Level by Level: Standard BFS Solution456. 132 PatternMedium4 Approaches: BF O(n^3), BF O(n^2), TreeMap, Monotonic Stack509. Fibonacci NumberEasy9 Fibonacci Algorithms: the Most Complete Solutions All In One with Image Explanation617. Merge Two Binary TreesEasy4 Approaches: Recursion, Iteration, BFS and DFS658. Find K Closest ElementsMedium4 Approaches: Two Pointers, Sorting, Priority Queue and Binary Search680. Valid Palindrome IIEasy3 Approaches: Brute Force, Recursion and Two Pointers692. Top K Frequent WordsMedium2 Approaches: HashMap + Sort and Priority Queue729. My Calendar IMedium3 Approaches: Brute Force, Binary Search, Segment Tree746. Min Cost Climbing StairsEasyFibonacci Numbers: 9 Approaches: Recursion, DP, Math, Matrix763. Partition LabelsMediumGreedy Solution with Easy Detailed Explanation856. Score of ParenthesesMediumThe Tricky and Clean Solution: Replace Core by 1858. Mirror ReflectionMediumWhat If the Ray Not Reflected and Expand the Room with Image Explanation881. Boats to Save PeopleMediumGreedy: Let the Heaviest Match the Lightest, if Not Matched, Let it Alone895. Maximum Frequency StackHardHashMap Solution with Detailed Explanation923. 3Sum With MultiplicityMedium5 Approaches: BF, Three Pointers, TreeMap, Count, DP946. Validate Stack SequencesMedium4 Approaches: Stack, Array, Greedy and O(n) Time O(1) Space947. Most Stones Removed with Same Row or ColumnMediumIt is Literally a Graph: DFS and Union Find)991. Broken CalculatorMediumGreedy: Reverse Thinking with Binary Algorithm1029. Two City SchedulingMediumGreedy: Sorting the Costs Array by What?1091. Shortest Path in Binary MatrixMediumWhy Use BFS? Search Every Possible Path vs Search A Possible Path1137. N-th Tribonacci NumberEasyAny Language Beats 100% with Time O(1) Solution1249. Minimum Remove to Make Valid ParenthesesMediumStack Solution with Easy Detailed Explanation1302. Deepest Leaves SumMedium2 Approaches: BFS(Level Order Travesal) and DFS(Get Max Depth, then Traversal)1631. Path With Minimum EffortMedium3 Approaches: BFS(Dijkstra), Binary Search, Union Find1641. Count Sorted Vowel StringsMediumImage Explanation: Distributing N Balls into 5 Boxes, Some Boxes May Be Empty1642. Furthest Building You Can ReachMediumPriority Queue + Greedy: Consider Ladder as a One-time Unlimited Bricks1663. Smallest String With A Given Numeric ValueMediumGreedy O(n) Solution with Image Explaination1721. Swapping Nodes in a Linked ListMedium3 Approaches: Swapping Values and Swapping Nodes with Image Explanation1780. Check if Number is a Sum of Powers of ThreeEasy3 Approaches: Tricky, Recursive and Base 3 Conversion1834. Single-Threaded CPUMediumHow to Maintain the Enqueued Tasks? Sorting the array then Priority Queue2215. Find the Difference of Two ArraysEasyJava HashSet Solution2475. Number of Unequal Triplets in ArrayEasyThe Fastest O(n) Solution: Math Combinations