leetcode 101 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 {
public:
    bool isSymmetric(TreeNode* root) {
        if(root == NULL)
            return true;
        return dfs(root->left, root->right);
    }
    bool dfs(TreeNode *lt, TreeNode *rt)
    {
        if(lt == NULL && rt == NULL)
            return true;
        if(lt && rt && lt->val == rt->val)
            return dfs(lt->left, rt->right) && dfs(lt->right, rt->left);
        return false;
    }
};