cs刷题帖

4/5
652. Find Duplicate Subtrees
687. Longest Univalue Path
637. Average of Levels in Binary Tree

4/10
993. Cousins in Binary Tree
107. Binary Tree Level Order Traversal II
226. Invert Binary Tree
671. Second Minimum Node In a Binary Tree
35. Search Insert Position
139. Word Break

amazon发了邮件给我让我继续等 所以从今天开始打算刷amazon vo的面经了 加油

78. Subsets
4/15
backtracking 的题
发现如果返回的是 数组一样长度的 for（int i = 0;...)
如果是 返回不一样长度的 （int i = start..) + boolean visited[]
如果有重复且避免  
for（int i = ；，，，）
if（i> 0  && nums[i] ==nums[i-1]) continue; // skip repeated element and avoid repeated calculation;
90. Subsets II
46. Permutations
47. Permutations II
39. Combination Sum
40. Combination Sum II
131. Palindrome Partitioning