LeetCode算法题目解答汇总
本文转自《四火的唠叨》
只要不是特别忙或者特别不方便，最近一直保持着每天做几道算法题的规律，到后来随着难度的增加，每天做的题目越来越少。我的初衷就是练习，因为一方面我本身算法基础并不好，再一方面是因为工作以后传统意义上所谓算法的东西接触还是太少。为了题目查找方便起见，我把之前几篇陆陆续续贴出来的我对LeetCode上面算法题的解答汇总在下面，CTRL+F就可以比较方便地找到。由于LeetCode上的题在不断更新，因此我也会不定期地更新。下面表格里面的Acceptance和Difficulty的Easy/Medium/Hard的分类都是来自LeetCode上面的数据，而Difficulty括号里面的数值和Frequency则来自这个文档。另外，LeetCode数据库的那十道题（截止到目前）我记录在这里。
总体来说，做LeetCode的题目收获还是很大的。而这种可以很快获得代码正确性和性能即使的反馈的方式，对算法提高也是很有帮助的。有的题目困难，主要包括两方面的原因，有的是思路比较怪异，用常规思路去解题往往时间复杂度或者空间复杂度过高，还有的则是需要考虑的情况比较复杂，case众多，很容易遗漏。
| Title | Acceptance | Difficulty | Frequency |
|---|---|---|---|
| Palindrome Number | 28.8% | Easy (2) | 2 |
| ZigZag Conversion | 23.4% | Easy (3) | 1 |
| Valid Sudoku | 27.6% | Easy (2) | 2 |
| Add Binary | 25.5% | Easy (2) | 4 |
| Valid Parentheses | 28.2% | Easy (2) | 5 |
| Valid Palindrome | 22.2% | Easy (2) | 5 |
| Balanced Binary Tree | 32.5% | Easy (1) | 2 |
| Valid Number | 11.0% | Easy (2) | 5 |
| Symmetric Tree | 31.6% | Easy (1) | 2 |
| String to Integer (atoi) | 14.2% | Easy (2) | 5 |
| Same Tree | 41.8% | Easy (1) | 1 |
| Binary Tree Level Order Traversal | 30.6% | Easy (3) | 4 |
| Binary Tree Level Order Traversal II | 31.0% | Easy (3) | 1 |
| Roman to Integer | 33.9% | Easy (2) | 4 |
| Reverse Integer | 39.8% | Easy (2) | 3 |
| Remove Nth Node From End of List | 29.3% | Easy (2) | 3 |
| Remove Element | 33.0% | Easy (1) | 4 |
| Remove Duplicates from Sorted List | 34.7% | Easy (1) | 3 |
| Climbing Stairs | 34.0% | Easy (2) | 5 |
| Remove Duplicates from Sorted Array | 32.2% | Easy (1) | 3 |
| Plus One | 31.4% | Easy (1) | 2 |
| Path Sum | 30.4% | Easy (1) | 3 |
| Pascal's Triangle II | 30.1% | Easy (2) | 1 |
| Pascal's Triangle | 31.1% | Easy (2) | 1 |
| Minimum Depth of Binary Tree | 29.4% | Easy (1) | 1 |
| Merge Two Sorted Lists | 33.2% | Easy (2) | 5 |
| Merge Sorted Array | 31.8% | Easy (2) | 5 |
| Maximum Depth of Binary Tree | 43.8% | Easy (1) | 1 |
| Longest Common Prefix | 27.0% | Easy (2) | 1 |
| Count and Say | 26.7% | Easy (2) | 2 |
| Length of Last Word | 29.0% | Easy (1) | 1 |
| Implement strStr() | 21.9% | Easy (4) | 5 |
| Divide Two Integers | 16.6% | Medium (4) | 3 |
| 3Sum | 16.7% | Medium (3) | 5 |
| Evaluate Reverse Polish Notation | 19.9% | Medium | |
| Find Minimum in Rotated Sorted Array | 31.7% | Medium | |
| Word Search | 19.8% | Medium (3) | 4 |
| Word Ladder | 18.4% | Medium (3) | 5 |
| Flatten Binary Tree to Linked List | 28.2% | Medium (3) | 3 |
| Gas Station | 25.9% | Medium | |
| Generate Parentheses | 31.4% | Medium (3) | 4 |
| Gray Code | 32.1% | Medium (4) | 2 |
| Word Break | 21.3% | Medium | |
| Validate Binary Search Tree | 25.9% | Medium (3) | 5 |
| Insertion Sort List | 25.3% | Medium | |
| Integer to Roman | 33.8% | Medium (3) | 4 |
| 4Sum | 21.4% | Medium (3) | 2 |
| Jump Game | 27.2% | Medium (3) | 2 |
| Add Two Numbers | 22.9% | Medium (3) | 4 |
| Anagrams | 23.9% | Medium (3) | 4 |
| Decode Ways | 16.2% | Medium (3) | 4 |
| Letter Combinations of a Phone Number | 26.4% | Medium (3) | 3 |
| Linked List Cycle | 35.7% | Medium | |
| Linked List Cycle II | 30.8% | Medium | |
| Best Time to Buy and Sell Stock | 31.2% | Medium (2) | 1 |
| Unique Paths II | 27.9% | Medium (3) | 3 |
| Longest Palindromic Substring | 20.6% | Medium (4) | 2 |
| Longest Substring Without Repeating Characters | 22.2% | Medium (3) | 2 |
| Unique Paths | 31.7% | Medium (2) | 3 |
| Unique Binary Search Trees II | 27.3% | Medium (4) | 1 |
| Unique Binary Search Trees | 36.5% | Medium (3) | 1 |
| Two Sum | 18.4% | Medium (2) | 5 |
| Convert Sorted List to Binary Search Tree | 27.3% | Medium (4) | 3 |
| Maximum Product Subarray | 15.9% | Medium | |
| Maximum Subarray | 34.0% | Medium (3) | 3 |
| Triangle | 26.6% | Medium (3) | 1 |
| Best Time to Buy and Sell Stock II | 36.6% | Medium (3) | 1 |
| Swap Nodes in Pairs | 32.4% | Medium (2) | 4 |
| Convert Sorted Array to Binary Search Tree | 32.9% | Medium (2) | 3 |
| Container With Most Water | 31.3% | Medium (3) | 2 |
| Minimum Path Sum | 31.0% | Medium (3) | 3 |
| Surrounded Regions | 14.2% | Medium (4) | 3 |
| Multiply Strings | 20.5% | Medium (4) | 3 |
| Sum Root to Leaf Numbers | 29.7% | Medium (2) | 4 |
| Subsets II | 27.0% | Medium (4) | 2 |
| Next Permutation | 25.4% | Medium (5) | 2 |
| 3Sum Closest | 27.0% | Medium (3) | 1 |
| Palindrome Partitioning | 25.9% | Medium (3) | 4 |
| Subsets | 27.9% | Medium (3) | 4 |
| Partition List | 27.0% | Medium (3) | 3 |
| Construct Binary Tree from Inorder and Postorder Traversal | 26.6% | Medium | |
| Construct Binary Tree from Preorder and Inorder Traversal | 26.5% | Medium | |
| Combinations | 30.0% | Medium (3) | 4 |
| Combination Sum II | 24.7% | Medium (4) | 2 |
| Path Sum II | 26.9% | Medium (2) | 2 |
| Permutation Sequence | 22.3% | Medium (5) | 1 |
| Permutations | 31.2% | Medium (3) | 4 |
| Sqrt(x) | 22.3% | Medium (4) | 4 |
| Combination Sum | 26.8% | Medium (3) | 3 |
| Populating Next Right Pointers in Each Node | 35.3% | Medium (3) | 3 |
| Spiral Matrix II | 30.8% | Medium (3) | 2 |
| Pow(x, n) | 25.9% | Medium (3) | 5 |
| Spiral Matrix | 20.6% | Medium (4) | 2 |
| Sort List | 20.6% | Medium | |
| Clone Graph | 23.0% | Medium | |
| Remove Duplicates from Sorted Array II | 30.6% | Medium (2) | 2 |
| Sort Colors | 32.1% | Medium (4) | 2 |
| Remove Duplicates from Sorted List II | 24.8% | Medium (3) | 3 |
| Binary Tree Zigzag Level Order Traversal | 26.5% | Medium (4) | 3 |
| Binary Tree Preorder Traversal | 35.5% | Medium | |
| Reorder List | 20.4% | Medium | |
| Restore IP Addresses | 20.5% | Medium (3) | 3 |
| Single Number II | 33.8% | Medium | |
| Reverse Linked List II | 26.1% | Medium (3) | 2 |
| Single Number | 45.6% | Medium | |
| Reverse Words in a String | 14.0% | Medium | |
| Simplify Path | 19.9% | Medium (3) | 1 |
| Rotate Image | 31.2% | Medium (4) | 2 |
| Rotate List | 22.0% | Medium (3) | 2 |
| Binary Tree Inorder Traversal | 35.5% | Medium (4) | 3 |
| Set Matrix Zeroes | 30.8% | Medium (3) | 5 |
| Search a 2D Matrix | 31.2% | Medium (3) | 3 |
| Search for a Range | 27.4% | Medium (4) | 3 |
| Search Insert Position | 34.9% | Medium (2) | 2 |
| Search in Rotated Sorted Array II | 30.9% | Medium (5) | 3 |
| Text Justification | 14.0% | Hard (4) | 2 |
| Search in Rotated Sorted Array | 28.6% | Hard (4) | 3 |
| Binary Tree Maximum Path Sum | 20.2% | Hard (4) | 2 |
| Reverse Nodes in k-Group | 24.9% | Hard (4) | 2 |
| Binary Tree Postorder Traversal | 31.0% | Hard | |
| Candy | 19.3% | Hard | |
| Edit Distance | 25.5% | Hard (4) | 3 |
| Recover Binary Search Tree | 23.7% | Hard (4) | 2 |
| Populating Next Right Pointers in Each Node II | 30.7% | Hard (4) | 2 |
| Permutations II | 25.0% | Hard (4) | 2 |
| Best Time to Buy and Sell Stock III | 22.4% | Hard (4) | 1 |
| Palindrome Partitioning II | 18.3% | Hard (4) | 3 |
| N-Queens II | 33.9% | Hard (4) | 3 |
| Substring with Concatenation of All Words | 18.1% | Hard (3) | 1 |
| Sudoku Solver | 20.9% | Hard (4) | 2 |
| N-Queens | 25.9% | Hard (4) | 3 |
| Minimum Window Substring | 18.1% | Hard (4) | 2 |
| Merge k Sorted Lists | 21.2% | Hard (3) | 4 |
| Merge Intervals | 20.9% | Hard (4) | 5 |
| Scramble String | 22.8% | Hard (5) | 2 |
| Trapping Rain Water | 28.9% | Hard (4) | 2 |
| Median of Two Sorted Arrays | 17.6% | Hard (5) | 3 |
| Maximal Rectangle | 21.5% | Hard (5) | 1 |
| Max Points on a Line | 11.2% | Hard | |
| LRU Cache | 14.1% | Hard | |
| Longest Valid Parentheses | 19.7% | Hard (4) | 1 |
| Longest Consecutive Sequence | 28.2% | Hard (4) | 3 |
| Copy List with Random Pointer | 23.5% | Hard | |
| Largest Rectangle in Histogram | 21.5% | Hard (5) | 2 |
| Jump Game II | 24.7% | Hard (4) | 2 |
| Interleaving String | 19.5% | Hard (5) | 2 |
| Insert Interval | 20.7% | Hard (4) | 5 |
| Wildcard Matching | 14.3% | Hard (5) | 3 |
| Distinct Subsequences | 25.0% | Hard (4) | 2 |
| Word Break II | 16.6% | Hard | |
| First Missing Positive | 22.6% | Hard (5) | 2 |
| Word Ladder II | 11.5% | Hard (1) | 1 |
| Find Minimum in Rotated Sorted Array II | 27.9% | Hard | |
| Regular Expression Matching | 20.2% | Hard (5) | 3 |
【2015-6-17】从上次贴出来我的解答以后，最新更新的题目，除了一些需要买书只能在电子书上面看解答的没法验证以外，凡是题目能够在线解答和验证答案的，我把我的全部和分析放在了下面。欢迎指正。
|
#
|
Title
|
Acceptance
|
Difficulty
|
|---|---|---|---|
| 226 | Invert Binary Tree | 37.6% | Easy |
| 225 | Implement Stack using Queues | 30.0% | Medium |
| 224 | Basic Calculator | 16.1% | Medium |
| 223 | Rectangle Area | 26.0% | Easy |
| 222 | Count Complete Tree Nodes | 19.8% | Medium |
| 221 | Maximal Square | 20.6% | Medium |
| 220 | Contains Duplicate III | 15.0% | Medium |
| 219 | Contains Duplicate II | 26.2% | Easy |
| 218 | The Skyline Problem | 17.0% | Hard |
| 217 | Contains Duplicate | 35.9% | Easy |
| 216 | Combination Sum III | 27.3% | Medium |
| 215 | Kth Largest Element in an Array | 27.4% | Medium |
| 214 | Shortest Palindrome | 16.3% | Hard |
| 213 | House Robber II | 26.1% | Medium |
| 212 | Word Search II | 15.0% | Hard |
| 211 | Add and Search Word – Data structure design | 20.9% | Medium |
| 210 | Course Schedule II | 19.1% | Medium |
| 209 | Minimum Size Subarray Sum | 23.1% | Medium |
| 208 | Implement Trie (Prefix Tree) | 25.0% | Medium |
| 207 | Course Schedule | 21.2% | Medium |
| 206 | Reverse Linked List | 32.0% | Easy |
| 205 | Isomorphic Strings | 24.2% | Easy |
| 204 | Count Primes | 18.9% | Easy |
| 203 | Remove Linked List Elements | 26.0% | Easy |
| 202 | Happy Number | 31.5% | Easy |
| 201 | Bitwise AND of Numbers Range | 27.2% | Medium |
| 200 | Number of Islands | 21.9% | Medium |
| 199 | Binary Tree Right Side View | 26.9% | Medium |
| 198 | House Robber | 28.8% | Easy |
| 191 | Number of 1 Bits | 37.3% | Easy |
| 190 | Reverse Bits | 28.3% | Easy |
| 189 | Rotate Array | 17.8% | Easy |
| 188 | Best Time to Buy and Sell Stock IV | 17.0% | Hard |
| 187 | Repeated DNA Sequences | 19.2% | Medium |
| 186 | Reverse Words in a String II | 31.1% | Medium |
| 179 | Largest Number | 15.7% | Medium |
| 174 | Dungeon Game | 17.5% | Hard |
| 173 | Binary Search Tree Iterator | 29.2% | Medium |
| 172 | Factorial Trailing Zeroes | 28.3% | Easy |
| 171 | Excel Sheet Column Number | 36.6% | Easy |
| 170 | Two Sum III – Data structure design | 24.7% | Easy |
| 169 | Majority Element | 34.9% | Easy |
| 168 | Excel Sheet Column Title | 18.1% | Easy |
| 167 | Two Sum II – Input array is sorted | 43.3% | Medium |
| 166 | Fraction to Recurring Decimal | 12.6% | Medium |
| 165 | Compare Version Numbers | 15.1% | Easy |
| 164 | Maximum Gap | 24.3% | Hard |
| 163 | Missing Ranges | 24.0% | Medium |
| 162 | Find Peak Element | 31.4% | Medium |
| 161 | One Edit Distance | 24.3% | Medium |
| 160 | Intersection of Two Linked Lists | 28.5% | Easy |
| 159 | Longest Substring with At Most Two Distinct Characters | 30.3% | Hard |
| 158 | Read N Characters Given Read4 II – Call multiple times | 22.2% | Hard |
| 157 | Read N Characters Given Read4 | 29.9% | Easy |
| 156 | Binary Tree Upside Down | 34.4% | Medium |
| 155 | Min Stack | 18.3% | Easy |
【Updated：12/15/2015】227到310题
|
#
|
Title
|
Acceptance
|
Difficulty
|
|---|---|---|---|
| 310 | Minimum Height Trees | 24.0% | Medium |
| 309 | Best Time to Buy and Sell Stock with Cooldown | 33.7% | Medium |
| 307 | Range Sum Query – Mutable | 15.5% | Medium |
| 306 | Additive Number | 23.2% | Medium |
| 304 | Range Sum Query 2D – Immutable | 20.3% | Medium |
| 303 | Range Sum Query – Immutable | 23.9% | Easy |
| 301 | Remove Invalid Parentheses | 28.6% | Hard |
| 300 | Longest Increasing Subsequence | 31.8% | Medium |
| 299 | Bulls and Cows | 25.9% | Easy |
| 297 | Serialize and Deserialize Binary Tree | 24.2% | Medium |
| 295 | Find Median from Data Stream | 19.7% | Hard |
| 292 | Nim Game | 50.0% | Easy |
| 290 | Word Pattern | 27.0% | Easy |
| 289 | Game of Life | 32.2% | Medium |
| 287 | Find the Duplicate Number | 36.0% | Hard |
| 284 | Peeking Iterator | 31.8% | Medium |
| 283 | Move Zeroes | 42.3% | Easy |
| 282 | Expression Add Operators | 21.5% | Hard |
| 279 | Perfect Squares | 29.8% | Medium |
| 278 | First Bad Version | 21.0% | Easy |
| 275 | H-Index II | 31.7% | Medium |
| 274 | H-Index | 27.1% | Medium |
| 273 | Integer to English Words | 16.9% | Medium |
| 268 | Missing Number | 37.5% | Medium |
| 264 | Ugly Number II | 24.5% | Medium |
| 263 | Ugly Number | 34.6% | Easy |
| 260 | Single Number III | 40.7% | Medium |
| 258 | Add Digits | 47.6% | Easy |
| 257 | Binary Tree Paths | 24.9% | Easy |
| 242 | Valid Anagram | 39.1% | Easy |
| 241 | Different Ways to Add Parentheses | 30.6% | Medium |
| 240 | Search a 2D Matrix II | 31.4% | Medium |
| 239 | Sliding Window Maximum | 24.8% | Hard |
| 238 | Product of Array Except Self | 39.5% | Medium |
| 237 | Delete Node in a Linked List | 44.0% | Easy |
| 236 | Lowest Common Ancestor of a Binary Tree | 27.7% | Medium |
| 235 | Lowest Common Ancestor of a Binary Search Tree | 37.9% | Easy |
| 234 | Palindrome Linked List | 25.3% | Easy |
| 233 | Number of Digit One | 22.6% | Medium |
| 232 | Implement Queue using Stacks | 33.8% | Easy |
| 231 | Power of Two | 33.3% | Easy |
| 230 | Kth Smallest Element in a BST | 34.0% | Medium |
| 229 | Majority Element II | 24.2% | Medium |
| 228 | Summary Ranges | 21.6% | Easy |
| 227 | Basic Calculator II | 22.2% | Medium |
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