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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
	List<String> list = new ArrayList<>();
    public int sumNumbers(TreeNode root) {
        sumNumbers(root,"");
        int sum = 0;
        for(String s:list){
        	sum += Integer.parseInt(s);
        }
        return sum;
    }
    
    private void sumNumbers(TreeNode root,String str){
    	if(root==null) return;
    	String s = str+root.val;
    	if(root.left == null&& root.right == null){
    		list.add(s);
    		return;
    	}
    	sumNumbers(root.left,s);
    	sumNumbers(root.right,s);
    }
}

[LeetCode]Sum Root to Leaf Numbers