【树】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.

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;
};