129. Sum Root to Leaf Numbers

Posted 2021-03-11 beiyeqingteng

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.

Note: A leaf is a node with no children.

Example:

Input: [1,2,3]
    1
   /   2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   /   9   0
 / 5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 class Solution {
11     public int sumNumbers(TreeNode root) {
12        int[] total = new int[]{ 0 }; 
13         helper(root, 0, total);
14         return total[0];
15     }
16     
17     private void helper(TreeNode root, int current, int[] total) {
18         if (root == null) return;
19         current = current * 10 + root.val;
20         if (root.left == null && root.right == null) {
21             total[0] += current;
22         }
23         helper(root.left, current, total);
24         helper(root.right, current, total);
25     }
26 }