判断二叉树是否对称

判断二叉树是否对称

import java.util.*;

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

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    public boolean robot(TreeNode left,TreeNode right){
        if(left==null && right==null){
            return true;
        }else{
            if(left==null || right==null){
                return false;
            }
        }
        return left.val==right.val && robot(left.left,right.right) && robot(left.right,right.left);
    }
    public boolean isSymmetric(TreeNode root) {
        if(root==null){
            return true;
        }
        return robot(root.left,root.right);
    }
}