CC150 3.6

3.6 Write a program to sort a stack in ascending order. You should not make any assumptions about how the stack is implemented. The following are the only functions that should be used to write this program: push | pop | peek | isEmpty.

interface Stack<T>
{
  push(T t);
  T pop();
  T peek();
  boolean isEmpty();
}

// Sort a stack?
// Does it mean changing the order of elements in the stack?
// What about popping all elements out to a list, sorting, and pushing back?

sort(Stack<T> stack)
{

  Stack<T> temp = initStack();
  Stack<T> toReturn = initStack();
  
  while (!stack.isEmpty())
  {
    T t = stack.pop();
    while (!toReturn.isEmpty() && t > toReturn.peek())
    {
      temp.push(toReturn.pop());
    }
    toReturn.push(t);
    while (!temp.isEmpty())
    {
      toReturn.push(temp.pop());
    }
  }
  
  return toReturn;
}