leetcode-Symmetric Tree

Difficulty: Easy

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3

/**
 * 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 {
    bool helper(TreeNode *root1,TreeNode *root2){
        if(!root1&&!root2)
            return true ;
        if(!root1||!root2)
            return false;
        if(root1->val==root2->val)
            return helper(root1->left,root2->right)&&helper(root1->right,root2->left);
        return false;    
    }
    
public:
    bool isSymmetric(TreeNode* root) {
        if(!root)
            return true;
        return helper(root->left,root->right);    
    }
};