题解 | #牛奶产量总和#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    public static int result = 0;
    public int sumNumbers (TreeNode root) {
        // write code here
        if(root == null){
            return result;
        }
        preOrder(root,root.val);
        return result;
    }

    public void preOrder(TreeNode node,int sum){
        if(node.left == null && node.right == null){
            result += sum;
            return;
        }

        if(node.left != null){
            preOrder(node.left,sum * 10 +node.left.val);
        }
       
        if(node.right != null){
            preOrder(node.right,sum * 10 + node.right.val);
        }
    }
}