145. Binary Tree Postorder Traversal
145. Binary Tree Postorder Traversal
# Definition for a binary tree
Tree
111. Minimum Depth of Binary Tree
111. Minimum Depth of Binary Tree
DFS
# Definition for a
255. Verify Preorder Sequence in Binary Search Tree
255. Verify Preorder Sequence in Binary Search Tree
遞迴（超時）
114. Flatten Binary Tree to Linked List
114. Flatten Binary Tree to Linked List
這一是後續遍歷很經典的一道題目，體現了後續遍歷很重要的一個精神，當後續遍歷到一半，
429. N-ary Tree Level Order Traversal
429. N-ary Tree Level Order Traversal
可以先做這題 116. Populating Next
543. Diameter of Binary Tree
543. Diameter of Binary Tree
這一題和 124. Binary Tree Maximum
417. Pacific Atlantic Water Flow
417. Pacific Atlantic Water Flow
廣度優先搜索
BFS 也可以利用一次把多個點加入 queue 後再開始出發，
113. Path Sum II
113. Path Sum II
這一題比較困難的是，雖然是樹的遍歷加上回溯法。
# Definition for a binary
104. Maximum Depth of Binary Tree
104. Maximum Depth of Binary Tree
# Definition for a binary
752. Open the Lock
752. Open the Lock
class Solution:
def openLock(self, deadends: