题解 | #二叉树根节点到叶子节点的所有路径和#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    public int sumNumbers (TreeNode root) {
        // write code here
         if (root == null) {
            return 0;
        }
        doSumNumbers(root, "0");
        return sum;
    }
    
     Integer sum = 0;

    // 先序遍历二叉树，遇到子树左右节点为空，则表示到叶子节点。
    public void doSumNumbers(TreeNode root, String before) {
        // write code here
        String num = String.valueOf(root.val);
        if (root.left == null && root.right == null) {
            sum += Integer.parseInt(before + num);
            System.out.println(sum);
        }
        if (root.left != null) {
            doSumNumbers(root.left, before + num);
        }
        if (root.right != null) {
            doSumNumbers(root.right, before + num);
        }
    }

}