129. 求根到叶子节点数字之和

class Solution:
    def sumNumbers(self, root: TreeNode) -> int:
        def sums(root,pre):
            if not root:
                return 0
            total=pre*10+root.val
            if not root.left and not root.right:
                return total
            else:
                return sums(root.left,total)+sums(root.right,total)
        return sums(root,0)

简单递归，深度优先搜索