这个重点题目是把Leetcode前400题进行精简，划分精简规则如下：
删除不常考，面试低频出现题目
删除重复代码题目（例：链表反转206题，代码在234题出现过）
删除过于简单题目（例：100题：Same Tree）
删除题意不同，代码基本相同题目（例：136 & 389，保留一个）
所有题目尽量保证客观公正，只是按大概率删除不常考题目，很多题目面经出现过， 但出现次数属于个位数或者只有一两家出现进行删除。所以如在面试中出现删除题目概不负责，这只是从概率上删除低频，简单题目。 旨在减轻大家的刷题负担，从400题减少到250题。
适用人群：有一定刷题基础，算法基础，二刷人群。
建议：400题全部刷完，再精刷这250题。
题号 题目名称
1 Two Sum
3 Longest Substring Without Repeating Characters
4 Median of Two Sorted Arrays
5 Longest Palindromic Substring
7 Reverse Integer
8 String to Integer (atoi)
10 Regular Expression Matching
11 Container With Most Water
12 Integer to Roman
13 Roman to Integer
15 3Sum
17 Letter Combinations of a Phone Number
18 4Sum
20 Valid Parentheses
22 Generate Parentheses
23 Merge k Sorted Lists
26 Remove Duplicates from Sorted Array
27 Remove Element
28 Implement strStr()
29 Divide Two Integers
31 Next Permutation
32 Longest Valid Parentheses
33 Search in Rotated Sorted Array
34 Find First and Last Position of Element in Sorted Array
35 Search Insert Position
36 Valid Sudoku
37 Sudoku Solver
38 Count and Say
39 Combination Sum
40 Combination Sum II
41 First Missing Positive
42 Trapping Rain Water
43 Multiply Strings
44 Wildcard Matching
45 Jump Game II
46 Permutations
47 Permutations II
48 Rotate Image
49 Group Anagrams
50 Pow(x, n)
51 N-Queens
52 N-Queens II
53 Maximum Subarray
54 Spiral Matrix
55 Jump Game
56 Merge Intervals
57 Insert Interval
59 Spiral Matrix II
60 Permutation Sequence
62 Unique Paths
64 Minimum Path Sum
65 Valid Number
66 Plus One
67 Add Binary
68 Text Justification
69 Sqrt(x)
70 Climbing Stairs
71 Simplify Path
72 Edit Distance
74 Search a 2D Matrix
75 Sort Colors
76 Minimum Window Substring
77 Combinations
78 Subsets
79 Word Search
80 Remove Duplicates from Sorted Array II
81 Search in Rotated Sorted Array II
82 Remove Duplicates from Sorted List II
84 Largest Rectangle in Histogram
85 Maximal Rectangle
88 Merge Sorted Array
90 Subsets II
91 Decode Ways
96 Unique Binary Search Trees
98 Validate Binary Search Tree
101 Symmetric Tree
104 Maximum Depth of Binary Tree
108 Convert Sorted Array to Binary Search Tree
110 Balanced Binary Tree
111 Minimum Depth of Binary Tree
112 Path Sum
113 Path Sum II
115 Distinct Subsequences
116 Populating Next Right Pointers in Each Node
117 Populating Next Right Pointers in Each Node II
121 Best Time to Buy and Sell Stock
122 Best Time to Buy and Sell Stock II
123 Best Time to Buy and Sell Stock III
124 Binary Tree Maximum Path Sum
125 Valid Palindrome
126 Word Ladder II
127 Word Ladder
128 Longest Consecutive Sequence
130 Surrounded Regions
133 Clone Graph
134 Gas Station
138 Copy List with Random Pointer
139 Word Break
140 Word Break II
142 Linked List Cycle II
146 LRU Cache
149 Max Points on a Line
150 Evaluate Reverse Polish Notation
152 Maximum Product Subarray
153 Find Minimum in Rotated Sorted Array
154 Find Minimum in Rotated Sorted Array II
155 Min Stack
157 Read N Characters Given Read4
158 Read N Characters Given Read4 II - Call multiple times
161 One Edit Distance
162 Find Peak Element
163 Missing Ranges
168 Excel Sheet Column Title
171 Excel Sheet Column Number
173 Binary Search Tree Iterator
174 Dungeon Game
186 Reverse Words in a String II
188 Best Time to Buy and Sell Stock IV
189 Rotate Array
191 Number of 1 Bits
198 House Robber
200 Number of Islands
201 Bitwise AND of Numbers Range
202 Happy Number
204 Count Primes
205 Isomorphic Strings
207 Course Schedule
208 Implement Trie (Prefix Tree)
209 Minimum Size Subarray Sum
210 Course Schedule II
211 Add and Search Word - Data structure design
212 Word Search II
213 House Robber II
214 Shortest Palindrome
215 Kth Largest Element in an Array
216 Combination Sum III
217 Contains Duplicate
218 The Skyline Problem
219 Contains Duplicate II
220 Contains Duplicate III
221 Maximal Square
224 Basic Calculator
225 Implement Stack using Queues
226 Invert Binary Tree
227 Basic Calculator II
228 Summary Ranges
230 Kth Smallest Element in a BST
231 Power of Two
232 Implement Queue using Stacks
235 Lowest Common Ancestor of a Binary Search Tree
236 Lowest Common Ancestor of a Binary Tree
238 Product of Array Except Self
239 Sliding Window Maximum
240 Search a 2D Matrix II
241 Different Ways to Add Parentheses
242 Valid Anagram
244 Shortest Word Distance II
245 Shortest Word Distance III
249 Group Shifted Strings
251 Flatten 2D Vector
252 Meeting Rooms
253 Meeting Rooms II
254 Factor Combinations
256 Paint House
257 Binary Tree Paths
261 Graph Valid Tree
263 Ugly Number
264 Ugly Number II
265 Paint House II
268 Missing Number
269 Alien Dictionary
270 Closest Binary Search Tree Value
271 Encode and Decode Strings
273 Integer to English Words
274 H-Index
275 H-Index II
276 Paint Fence
277 Find the Celebrity
278 First Bad Version
279 Perfect Squares
280 Wiggle Sort
282 Expression Add Operators
283 Move Zeroes
284 Peeking Iterator
285 Inorder Successor in BST
286 Walls and Gates
287 Find the Duplicate Number
288 Unique Word Abbreviation
289 Game of Life
290 Word Pattern
291 Word Pattern II
293 Flip Game
294 Flip Game II
295 Find Median from Data Stream
296 Best Meeting Point
297 Serialize and Deserialize Binary Tree
298 Binary Tree Longest Consecutive Sequence
299 Bulls and Cows
300 Longest Increasing Subsequence
301 Remove Invalid Parentheses
302 Smallest Rectangle Enclosing Black Pixels
305 Number of Islands II
307 Range Sum Query - Mutable
308 Range Sum Query 2D - Mutable
309 Best Time to Buy and Sell Stock with Cooldown
311 Sparse Matrix Multiplication
312 Burst Balloons
314 Binary Tree Vertical Order Traversal
316 Remove Duplicate Letters
317 Shortest Distance from All Buildings
318 Maximum Product of Word Lengths
322 Coin Change
323 Number of Connected Components in an Undirected Graph
324 Wiggle Sort II
325 Maximum Size Subarray Sum Equals k
329 Longest Increasing Path in a Matrix
334 Increasing Triplet Subsequence
336 Palindrome Pairs
337 House Robber III
338 Counting Bits
339 Nested List Weight Sum
340 Longest Substring with At Most K Distinct Characters
341 Flatten Nested List Iterator
346 Moving Average from Data Stream
347 Top K Frequent Elements
348 Design Tic-Tac-Toe
350 Intersection of Two Arrays II
351 Android Unlock Patterns
352 Data Stream as Disjoint Intervals
353 Design Snake Game
354 Russian Doll Envelopes
355 Design Twitter
359 Logger Rate Limiter
361 Bomb Enemy
362 Design Hit Counter
364 Nested List Weight Sum II
367 Valid Perfect Square
374 Guess Number Higher or Lower
375 Guess Number Higher or Lower II
376 Wiggle Subsequence
377 Combination Sum IV
378 Kth Smallest Element in a Sorted Matrix
379 Design Phone Directory
380 Insert Delete GetRandom O(1)
381 Insert Delete GetRandom O(1) - Duplicates allowed
384 Shuffle an Array
385 Mini Parser
389 Find the Difference
394 Decode String
398 Random Pick Index