257. 二叉树的所有路径

问题描述

https://leetcode.cn/problems/binary-tree-paths/description/

解题思路

叶子结点时，添加到结果序列即可。

代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def binaryTreePaths(self, root: Optional[TreeNode]) -> List[str]:
        res = []
        def dfs(root, cur):
            if root is None:
                return
            cur += str(root.val)
            if root.left is None and root.right is None:
                res.append(cur)
            dfs(root.left, cur+'->' if root.left is not None else cur)
            dfs(root.right, cur+'->' if root.right is not None else cur)
        dfs(root, '')
        return res

 解法二

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def binaryTreePaths(self, root: Optional[TreeNode]) -> List[str]:
        res = []
        def dfs(root, last):
            if root is None:
                return
            if root.left is None and root.right is None:
                res.append(last + f'{root.val}')
                return
            dfs(root.left, last + f'{root.val}->')
            dfs(root.right, last + f'{root.val}->')
        dfs(root, "")
        return res