Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number. An example is the root-to-leaf path1->2->3which represents the number123. Find the total sum of a

class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }
}
public class Solution {
public int sumNumbers(TreeNode root) {
if(root==null)return 0;
return sumRoot(root,0);
}

private int sumRoot(TreeNode root, int sum) {
if(root==null)return 0;
sum=sum*10+root.val;//关键
if(root.left==null&&root.right==null)return sum;
return sumRoot(root.left, sum)+sumRoot(root.right, sum);//左右都要递归哦
}

}