LeetCode之Symmetric Tree

 /*采用递归法，分别对左右子树进行检查。*/
class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        if(root == nullptr || (root->left == nullptr && root->right == nullptr))
           return true;
        return isSymmetric(root->left, root->right);
    }
    
    bool isSymmetric(TreeNode *left, TreeNode *right){
        if(left == nullptr) return right == nullptr;
        if(right == nullptr) return left == nullptr;
        return left->val == right->val
        && isSymmetric(left->left, right->right)
        && isSymmetric(left->right, right->left);
    }
};