每日一题 leetcode 965. 单值二叉树 java

https://leetcode.cn/problems/univalued-binary-tree/

/**
 * 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 {
    int mo;
    boolean flag=true;
    public boolean isUnivalTree(TreeNode root) {
        if(root==null) return true;
        this.mo=root.val;
        return dfs(root);
    }
    public boolean dfs(TreeNode node){
        if(flag==false) return false;
        if(node==null)  return true;
        if(node.val!=mo){
            flag=false;
            return false;
        }    
        return dfs(node.left)&&dfs(node.right);
    }
}