is_subtree.cpp

// check sub tree n1 == sub tree n2
bool isSame(const TreeNode* n1, const TreeNode* n2){
	if( n1 == NULL && n2 == NULL )
		return true;

	if( n1 == NULL || n2 == NULL )
		return false;

	if( n1->data != n2->data )
		return false;

	return isSame(n1->leftChild, n2->leftChild) && isSame(n1->rightChild, n2->rightChild);
}

bool isSubTree(const TreeNode *n1, const TreeNode *n2){
	if( n1 == NULL){
		return false; // the bigger tree is empty, so t2 is not subtree of t1
	}

	if( n1->data == n2->data){
		if( isSame(n1, n2))
			return true;
	}

	return isSubTree(n1->leftChild, n2) || isSubTree(n2->rightChild, n2);
}