LeetCode力扣之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

.

package leetCode;

/**
* Created by lxw, liwei4939@126.com on 2018/3/26.
*/
public class L129_SumRootToLeafNumbers {

public int sumNumbers(TreeNode root){
return helper(root, 0);
}

public int helper(TreeNode root, int curSum){
if (root == null){
return 0;
}

curSum = curSum * 10 + root.val;
if (root.left == null && root.right == null){
return curSum;
}
return helper(root.left, curSum) + helper(root.right, curSum);
}
}