0129. Sum Root to Leaf Numbers

# 129. Sum Root to Leaf Numbers#

## 题目 #

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.

Note: A leaf is a node with no children.

Example:

``````Input: [1,2,3]
1
/ \
2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
``````

Example 2:

``````Input: [4,9,0,5,1]
4
/ \
9   0
/ \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.
``````

## 解题思路 #

• 这一题是第 257 题的变形题，第 257 题要求输出每条从根节点到叶子节点的路径，这一题变成了把每一个从根节点到叶子节点的数字都串联起来，再累加每条路径，求出最后的总和。实际做题思路基本没变

## 代码 #

``````
package leetcode

import (
"strconv"
)

/**
* Definition for a binary tree node.
* type TreeNode struct {
*     Val int
*     Left *TreeNode
*     Right *TreeNode
* }
*/
func sumNumbers(root *TreeNode) int {
res, nums := 0, binaryTreeNums(root)
for _, n := range nums {
num, _ := strconv.Atoi(n)
res += num
}
return res
}

func binaryTreeNums(root *TreeNode) []string {
if root == nil {
return []string{}
}
res := []string{}
if root.Left == nil && root.Right == nil {
return []string{strconv.Itoa(root.Val)}
}
tmpLeft := binaryTreeNums(root.Left)
for i := 0; i < len(tmpLeft); i++ {
res = append(res, strconv.Itoa(root.Val)+tmpLeft[i])
}
tmpRight := binaryTreeNums(root.Right)
for i := 0; i < len(tmpRight); i++ {
res = append(res, strconv.Itoa(root.Val)+tmpRight[i])
}
return res
}

``````

Sep 6, 2020