题解 | #牛群的对称排列#

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 {
    /**
     * 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 
     * @return bool布尔型
     */
    public boolean isSymmetric (TreeNode root) {
        // write code here
        if(root==null) return true;
        return get(root.left,root.right);
    }
    public boolean get(TreeNode first,TreeNode last){
        if(first==null&&last==null) return true;
        if(first==null&&last!=null||first!=null&&last==null||first.val!=last.val) return false;
        
        return get(first.left,last.right)&&get(first.right,last.left);
    }
}