Leetcode 257. Binary Tree Paths

Problem

Given the root of a binary tree, return all root-to-leaf paths in any order.

A leaf is a node with no children.

Algorithm

Use dfs search to save the path.

Code

# 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]:
        if not root:
            return []

        if not root.left and not root.right:
            return [str(root.val)]
        
        ans = []
        save = []
        def dfs(node: TreeNode, depth):
            if not node.left and not node.right:
                s = ""
                for i in range(depth):
                    s += str(save[i]) + "->"
                ans.append(s + str(node.val))
                return
            if len(save) <= depth:
                save.append(node.val)
            else:
                save[depth] = node.val
            if node.left:
                dfs(node.left, depth+1)
            if node.right:
                dfs(node.right, depth+1)

        dfs(root, 0)
        return ans