题解 | #牛的奶量统计#

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 boolean flag = false;//声明一个变量，观察状态
    /**
     * 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
     * @param targetSum int整型
     * @return bool布尔型
     */
    public boolean hasPathSum (TreeNode root, int targetSum) {
        if (root == null) {//base case
            return false;
        }
        if (root.left == null && root.right == null) {
            if (root.val == targetSum) {
                return true;
            } else {
                return false;
            }
        }
        dfs(root, targetSum);//执行主方法
        return flag;
    }
    public void dfs(TreeNode root, int target) {
        if (root.left == null && root.right == null) {
            if (root.val == target) {
                flag = true;
            }
        }
        if (root.left != null) {
            dfs(root.left, target - root.val);
        }
        if (root.right != null) {
            dfs(root.right, target - root.val);
        }

    }
}