【LeetCode】129. Sum Root to Leaf Numbers 解題報告（Python）

【LeetCode】129. Sum Root to Leaf Numbers 解題報告（Python）

標籤（空格分隔）： LeetCode

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

題目描述：

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.

解題方法

這個題和Binary Tree Paths如出一轍，前個題是求路徑，這個題是把路徑按照10的倍數拼接在一塊兒，最後求和便可。

有個技巧就是res = 0當作參數傳給函數，那麼函數最後的結果不會影響到res，可是若是把res = [0]便可。

代碼：

# 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