leetcode-101. 对称二叉树

一、题目

二、思路

递归法：

三、代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution
{
public:
    bool isSymmetric(TreeNode *root)
    {
        if (root == nullptr)
        {
            return true;
        }
        return compare(root->left, root->right);
    }
    int compare(TreeNode *left, TreeNode *right)
    {
        if (left == nullptr && right == nullptr)
        {
            return true;
        }
        else if (left == nullptr && right != nullptr)
        {
            return false;
        }
        else if (left != nullptr && right == nullptr)
        {
            return false;
        }
        else if (left->val != right->val)
        {
            return false;
        }
        int x=compare(left->left,right->right);
        int y=compare(left->right,right->left);
        return x&&y;
    }
};