【LeetCode】 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 =
4000
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 helper(root, 0);
}

private int helper(TreeNode node, int num) {
if (node == null) {
return 0;
}
int temp = num * 10 + node.val;
if (node.left == null && node.right == null) {
return temp;
}
return helper(node.left, temp) + helper(node.right, temp);
}
}