题解 | #牛群的轴对称结构#

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 isSame(root.left, root.right);
    }
    private boolean isSame(TreeNode left, TreeNode right){
        if(left == null && right == null)return true;
        else if(left == null || right == null){
            return false;
        }else{
            if(left.val != right.val)return false;
            return isSame(left.left, right.right) && isSame(left.right, right.left);
        }
    }
}

当前层左右对称的时候需要递归判断子树是否对称