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

时间:2021-05-06 13:14:44

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

标签(空格分隔): LeetCode


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