【每日一题Day305】LC1448统计二叉树中好节点的数目 | dfs

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int goodNodes(TreeNode root) {
        return dfs(root, Integer.MIN_VALUE);
    }
    public int dfs(TreeNode root, int mx){
        if (root == null) return 0;
        int res = 0;
        if (root.val >= mx){
            res += 1;
            mx = root.val;
        }
        mx = Math.max(mx, root.val);
        res += dfs(root.left, mx);
        res += dfs(root.right, mx);
        return res;
    }
}