[leetcode]Symmetric Tree

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

 

But the following is not:

    1

   / \

  2   2

   \   \

   3    3

 

Note:
Bonus points if you could solve it both recursively and iteratively.

 

/**

 * Definition for binary tree

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    bool sym(TreeNode *root1, TreeNode *root2){

        if(!root1 && !root2) return true;

        if(!root1 || !root2) return false;

        

        if(root1->val != root2->val) return false;

        

        if(!sym(root1->left,root2->right)) return false;

        if(!sym(root1->right,root2->left)) return false;



        return true;

        

    }



    bool isSymmetric(TreeNode *root) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

        if(!root) return true;

        return sym(root->left, root->right);

    }

};