Medium

Pending
50 Pow(x, n)
141 Linked List Cycle
20 Valid Parentheses
160 Intersection of Two Linked Lists
105 Construct Binary Tree from Preorder and Inorder Traversal

102 Binary Tree Level Order Traversal
8 String to Integer (atoi)
13 Roman to Integer
79 Word Search
103 Binary Tree Zigzag Level Order Traversal
139 Word Break
172 Factorial Trailing Zeroes
101 Symmetric Tree
113 Path Sum II
11 Container With Most Water
208 Implement Trie (Prefix Tree)
274 H-Index

重点难点:(
49 Group Anagrams
151 Reverse Words in a String
131 Palindrome Partitioning
7 Reverse Integer
215 Kth Largest Element in an Array
206 Reverse Linked List

Done
230 Kth Smallest Element in a BST
(In order traversal, or recursive solution)

24 Swap Nodes in Pairs
(use dummy node.)

63 Unique Paths II

69 Sqrt(x)
(Binary search!)
155 Min Stack
(Keep an non-descending stack!)

16 3Sum Closest
15 3Sum
(pay attention to duplicates)

2 Add Two Numbers

189 Rotate Array
(two solutions, (yx) = (x'y')', pay attention to zero k)

5 Longest Palindromic Substring
(a DP method, use matrix to record s[i, j-i+1]; note the difference between 2D vector and 2D array.)

268 Missing Number
(several solutions, bit manipulation solution, "First missing positive" solution, an array of bool)

88 Merge Sorted Array
(from the end to beginning)

1 Two Sum
121 Best Time to Buy and Sell Stock
283 Move Zeroes (remain th orders)
100 Same Tree
3 Longest Substring Without Repeating Characters 98 Validate Binary Search Tree
26 Remove Duplicates from Sorted Array
(Pay attention to empty/too-short array)
110 Balanced Binary Tree
(compute the depth of a tree, if it is no balanced, return the depth as -1)