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.

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

.

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int sumNumbers(TreeNode root) {
return sumNumbers(root,0);
}
private int sumNumbers(TreeNode root, int sum){
if (root==null) return 0;
if(root.left==null&&root.right==null) return sum*10+root.val;
return sumNumbers(root.left,sum*10+root.val) + sumNumbers(root.right,sum*10+root.val);
}
}

总结：基本思路想到了，还需要整理更清晰。落实到代码上。