int LeftSum(Tree * t)
// postcondition: returns sum of all nodes in t that are left-children
{
    if (t == 0){
	return 0;
    }
    else if (t->left != 0){
	return t->left->info + LeftSum(t->left) + LeftSum(t->right);
    }
    else{
	return LeftSum(t->right):
    }
}

void PrintDepth(Tree * t, int d)
// postcondition: all nodes of t at depth d printed
{
    if (t != 0){
	if (d == 0){
	    cout << t->info << endl;
	}
	else{
	    PrintDepth(t->left,d-1);
	    PrintDepth(t->right,d-1);
	}
    }
}

void LevelOrder(Tree * t)
{
    if (t != 0){
	Queue<Tree *> q;	// queue of Tree pointers
	
	q.Enqueue(t);		// root is on queue to start
	while (! q.IsEmpty()){
	    q.Dequeue(t);
	    if (t != 0){
		cout << t->info << endl;
		q.Enqueue(t->left);
		q.Enqueue(t->right);
	    }
	}
    }
}


Tree * DoTree(int a[], int first, int last)
// precondition: a[first] <= a[first+1] <= ... <= a[last]
// postcondition: returns balanced search tree containing
//                a[first]...a[last]     
{
    if (first <= last){
	int mid = (first + last + 1);

	return new Node(a[mid],
			DoTree(a,first,mid-1);
			DoTree(a,mid+1,last));
    }
    return 0;
}