对称二叉树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    bool isSymmetricCore(TreeNode* node1,TreeNode* node2)
    {
        if(node1==nullptr&&node2==nullptr)
            return true;
        else if(node1==nullptr||node2==nullptr)
            return false;
        
        if(node1->val!=node2->val)
            return false;
        return isSymmetricCore(node1->left,node2->right)&&isSymmetricCore(node1->right,node2->left);
    }
public:
    bool isSymmetric(TreeNode* root) {
        if(root==nullptr)
            return true;
        
        return isSymmetricCore(root->left,root->right);
    }
};