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
bool isSymmetric(TreeNode *root)
{
if(root == NULL || (root->left == NULL && root->right == NULL))
{
return true;
}
return isSymmetricCore(root->left, root->right);
}
bool isSymmetricCore(TreeNode* left, TreeNode* right)
{
if((left == NULL && right != NULL) || (left != NULL && right == NULL))
{
return false;
}
else if(left == NULL && right == NULL)
{
return true;
}
else
{
if(left->val != right->val)
{
return false;
}
else
{
return isSymmetricCore(left->left, right->right) && isSymmetricCore(left->right, right->left);
}
}
}