[LeetCode]101. Symmetric Tree

Problem Description

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
[https://leetcode.com/problems/symmetric-tree/]

思路

递归左右两棵子树，判断是否对称

Code

package q101;

import TreeNode.TreeNode;
import TreeNode.Codec_TLE;

public class Solution {

    public static boolean isSymmetric(TreeNode root) {
        if(root==null) return true;
        return helper(root.left, root.right);
    }

    public static boolean helper(TreeNode left, TreeNode right) {
        if (left == null && right == null )
            return true;
        else if (left == null && right != null || left != null && right == null)
            return false;

        if (left.val == right.val) {
            return helper(left.left, right.right)
                    && helper(left.right, right.left);
        } else
            return false;
    }

    public static void main(String[] args) {
        TreeNode root = Codec_TLE.deserialize("1,2,3");
        System.out.print(isSymmetric(root));
    }

}