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 TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 
     */
    public int sumNumbers (TreeNode root) {
        int res = dfs(root, 0);
        return res;
    }

    public int dfs(TreeNode root, int sum) {
        //节点数为0或该子结点是空的
        if (root == null) {
            return 0 ;
        }

        //走到头了
        if (root.left == null && root.right == null) {
            return sum + root.val;
        }

        int left = dfs(root.left, (sum + root.val) * 10);
        int right = dfs(root.right, (sum + root.val) * 10);
        
        return left + right;
    }
}