LeetCode 257 - 二叉树的所有路径

class Solution:
    def binaryTreePaths(self, root: Optional[TreeNode]) -> List[str]:
        result = []
        nodeList = []
        # 列表推导式可用快速把列表变成字符串
        def listToStr():
            str_arr = '->'.join([str(x) for x in nodeList])
            result.append(str_arr)
        def binaryTreePathsIMPL(root: Optional[TreeNode]):
            #节点为空直接返回
            if not root:
                return
            # 节点不为空加入列表方便回溯
            nodeList.append(root.val)

            # 到达叶子节点后打印，同时弹出当前节点
            if not root.left and not root.right:
                listToStr()
                nodeList.pop()
                return
            
            # 递归
            binaryTreePathsIMPL(root.left)
            binaryTreePathsIMPL(root.right)

            # 完成左右子树的遍历后，弹出当前节点
            nodeList.pop()
        binaryTreePathsIMPL(root)
        return result