129. Sum Root to Leaf Numbers
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:
代码语言：javascript复制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.思路：
题目意思是根节点到叶子节点路劲构成一个整型数，对所有路劲求和，其实257,、112、113和现在的129题，都是一类模板题，只是稍作变形，都可以用递归或者迭代，从根节点访问到叶子节点，实质是先序遍历。
代码：
go：
代码语言：javascript复制/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func sumNumbers(root *TreeNode) int {
var res int
if root == nil {
return res
}
recursive(root, root.Val, &res)
return res
}
func recursive(node *TreeNode, sum int, res *int) {
if node.Left == nil && node.Right == nil {
*res = sum
}
if node.Left != nil {
recursive(node.Left, sum * 10 node.Left.Val, res)
}
if node.Right != nil {
recursive(node.Right, sum * 10 node.Right.Val, res)
}
}
