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。
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
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

转载请保持完整性并注明来源链接《四火的唠叨》

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