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);        }};