257. Binary Tree Paths

257. Binary Tree Paths

Easy

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

A leaf is a node with no children.

Example 1:

Input: root = [1,2,3,null,5]
Output: ["1->2->5","1->3"]

Example 2:

Input: root = [1]
Output: ["1"]

Constraints:

• The number of nodes in the tree is in the range [1, 100].
• -100 <= Node.val <= 100

 

# 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]:
        """
        
        """

        # 遍历
        def walkTreePaths(node: TreeNode, s: str):
            if node is None:
                return
            s += "->" + str(node.val)
            if node.left is None and node.right is None:
                result.append(s)
                return
            walkTreePaths(node.left, s)
            walkTreePaths(node.right, s)

        if root.left is None and root.right is None:
            return [str(root.val)]

        result = []
        if root.left is not None:
            walkTreePaths(root.left, str(root.val))
        if root.right is not None:
            walkTreePaths(root.right, str(root.val))
        return result