129. Sum Root to Leaf Numbers（从根节点加到叶子节点的和）

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

.

1 class Solution {
2     public int sumNumbers(TreeNode root) {
3      return sum(root,0);
4     }
5     private int sum(TreeNode root,int s) {
6         //s 上一层的累积和
7         if(root==null) return 0;
8         if(root.left==null && root.right==null) //遍历到叶子节点
9             return s*10+root.val;
10         return sum(root.left,s*10+root.val)+sum(root.right,s*10+root.val);
11     }
12 }