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.
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.
思路：
利用栈进行深度优先遍历。
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number}
*/
var sumNumbers = function(root) {
if(root==null){
return 0;
} function Node(treeNode,sum){
this.treeNode=treeNode;
this.sum=sum;
} var res=0,stack=[];
var n=new Node(root,root.val);
stack.push(n); while(stack.length!=0){
var p=stack.pop();
if(p.treeNode.left==null&&p.treeNode.right==null){
res+=p.sum;
}else{
if(p.treeNode.left!=null){
stack.push(new Node(p.treeNode.left,p.sum*10+p.treeNode.left.val))
}
if(p.treeNode.right!=null){
stack.push(new Node(p.treeNode.right,p.sum*10+p.treeNode.right.val))
}
}
} return res;
};