【LeetCode】129. Sum Root to Leaf Numbers 解题报告（Python）

标签（空格分隔）： LeetCode

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题目地址：https://leetcode.com/problems/sum-root-to-leaf-numbers/description/

题目描述：

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1

   / \

  2   3

The root-to-leaf path 1->2 represents the number 12.

The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

解题方法

这个题和Binary Tree Paths一模一样，前个题是求路径，这个题是把路径按照10的倍数拼接在一起，最后求和即可。

有个技巧就是res = 0当做参数传给函数，那么函数最后的结果不会影响到res，但是如果把res = [0]即可。

代码：

# Definition for a binary tree node.

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    def sumNumbers(self, root):

        """

        :type root: TreeNode

        :rtype: int

        """

        if root == None:

            return 0

        res = [0]

        self.dfs(root, res, root.val)

        return res[0]

    def dfs(self, root, res, path):

        if root.left == None and root.right == None:

            res[0] += path

        if root.left != None:

            self.dfs(root.left, res, path * 10 + root.left.val)

        if root.right != None:

            self.dfs(root.right, res, path * 10 + root.right.val)

日期

2018 年 2 月 25 日

【LeetCode】129. Sum Root to Leaf Numbers 解题报告（Python）的相关教程结束。