[LeetCode] 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.

[Solution].java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int[] sum = new int[1];
        dfs(0, sum, root);
        return sum[0];
    }

    public void dfs(int one, int[] sum, TreeNode root){
        if(root == null) return;
      one = one * 10 + root.val;
    	if(root.right == null && root.left == null){
    		sum[0] += one;
    		return;
    	}
    	if(root.right != null) dfs(one, sum, root.right);
    	if(root.left != null) dfs(one, sum, root.left);
    }
}