Question

I know how to sort an array but I haven’t sorted a stack before.
So please help. How can I sort a stack using the quicksort algorithm?
Thank you.

Answer 1

I know how to sort an array but I haven’t sort stack before.

The most efficient solution is probably to change the data structure to a list which allows random access and then sort the list. I.e., something like this:

1. Pop all elements of the stack into an array
2. Use the algorithm you do know and sort the array.
3. Push all elements back into the stack.

---

If you absolutely don’t want to use a list, you’ll perhaps find this solution interesting. (Stolen from here):

void sort(stack)
{
    type x;

    if (!isEmpty(stack)) {
        x = pop(stack);
        sort(stack);
        insert(x, stack);
    }           
}

void insert(x, stack)
{
    type y;

    if (!isEmpty(stack) && top(stack) < x) {
        y = pop(stack);
        insert(x, stack);
        push(y, stack);
    } else {
        push(x, stack);
    }
}