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

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     struct TreeNode *left; *     struct TreeNode *right; * }; */bool isTwoSym(struct TreeNode *leftRoot, struct TreeNode *rightRoot){    int leftR, rightR;    if(leftRoot == NULL && rightRoot == NULL)        return true;    else if(leftRoot == NULL && rightRoot != NULL)        return false;    else if(leftRoot != NULL && rightRoot == NULL)        return false;    else if(leftRoot->val == rightRoot->val)        {            leftR = isTwoSym(leftRoot->left, rightRoot->right);            rightR = isTwoSym(leftRoot->right, rightRoot->left);            return(leftR && rightR);        }    else        return false;}bool isSymmetric(struct TreeNode* root) {    bool left, right;    if(root == NULL)        return true;    else         return isTwoSym(root, root);}