剑指 Offer 28. 对称的二叉树

原题链接：剑指 Offer 28. 对称的二叉树

 

solution:     

class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        if(root == NULL) return true;
        return dfs(root->left,root->right);
    }

    bool dfs(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 false;
        return dfs(left->left,right->right) && dfs(left->right, right->left);
    }
};