Sum Root to Leaf Numbers

题目描述：

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.

题目比较简单，就是找到叶子节点，记录中间经过的值，到根节点的时候加入到sum中。

代码如下：

public class Solution {
    int sum=0;
	
	public int sumNumbers(TreeNode root) {
		if(root==null)
			return 0;
		subSumNumbers(root, 0);
		return sum;
    }
	
	public void subSumNumbers(TreeNode root,int num){
		if(root.left==null&&root.right==null)
			sum+=num*10+root.val;
		if(root.left!=null)
			subSumNumbers(root.left, num*10+root.val);
		if(root.right!=null)
			subSumNumbers(root.right, num*10+root.val);
	}
}