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.     1
  2.    / \
  3.   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.

Solution:

  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. public class Solution {
  11.   int total;
  13.   public int sumNumbers(TreeNode root) {
  14.     total = 0;
  15.     helper(root, 0);
  16.     return total;
  17.   }
  19.   void helper(TreeNode root, int sum) {
  20.     if (root == null) return;
  22.     sum = sum * 10 + root.val;
  24.     if (root.left == null && root.right == null) {
  25.       total += sum;
  26.       return;
  27.     }
  29.     helper(root.left, sum);
  30.     helper(root.right, sum);
  31.   }
  32. }