257. 二叉树的所有路径
1 # Definition for a binary tree node.
2 # class TreeNode:
3 # def __init__(self, val=0, left=None, right=None):
4 # self.val = val
5 # self.left = left
6 # self.right = right
7 class Solution:
8 def binaryTreePaths(self, root: TreeNode) -> List[str]:
9 path = ''
10 result = []
11 if not root: return result
12 self.traversal(root, path, result)
13 return result
14
15 def traversal(self, cur: TreeNode, path: str, result: List[str]) -> None:
16 path += str(cur.val)
17 # 若当前节点为leave，直接输出
18 if not cur.left and not cur.right:
19 result.append(path)
20 #return
21
22 if cur.left:
23 # + '->' 是隐藏回溯
24 #，貌似没有看到回溯的逻辑，其实不然，回溯就隐藏在traversal(cur->left, path + "->", result);中的 path + "->"。 每次函数调用完，path依然是没有加上"->" 的，这就是回溯了。
25 self.traversal(cur.left, path + '->', result)
26
27 if cur.right:
28 self.traversal(cur.right, path + '->', result)
513. 找树左下角的值
1 # Definition for a binary tree node.
2 # class TreeNode:
3 # def __init__(self, val=0, left=None, right=None):
4 # self.val = val
5 # self.left = left
6 # self.right = right
7 from collections import deque
8 class Solution:
9 def findBottomLeftValue(self, root):
10 if root is None:
11 return 0
12 queue = deque()
13 queue.append(root)
14 result = 0
15 while queue:
16 size = len(queue)
17 for i in range(size):
18 node = queue.popleft()
19 if i == 0:
20 result = node.val
21 if node.left:
22 queue.append(node.left)
23 if node.right:
24 queue.append(node.right)
25 return result
