/*  Three in One: Describe how you could use a single array to implement three stacks. */

​

using System;

public class Program

{

    public static void Main()

    {

        ArrayStack arrayStack = new ArrayStack(9);

        Console.WriteLine(arrayStack.Pop(1));

        Console.WriteLine(arrayStack.Pop(2));

        Console.WriteLine(arrayStack.Pop(3));

        arrayStack.Push(1,1);

        arrayStack.Push(2,2);

        arrayStack.Push(3,3);

        Console.WriteLine(arrayStack.Peek(1));

        Console.WriteLine(arrayStack.Peek(2));

        Console.WriteLine(arrayStack.Peek(3));

        Console.WriteLine(arrayStack.Pop(1));

        Console.WriteLine(arrayStack.Pop(2));

        Console.WriteLine(arrayStack.Pop(3));

        Console.WriteLine(arrayStack.Peek(1));

        Console.WriteLine(arrayStack.Peek(2));

        Console.WriteLine(arrayStack.Peek(3));

        arrayStack.Push(1,1);

        arrayStack.Push(1,2);

        arrayStack.Push(1,3);

        arrayStack.Push(1,4);

    }

}

​

public class ArrayStack

{

    private int[] threeStacks;  

    private int[] _min = new int[3];

    private int[] _max = new int[3];

    private int[] _pointer = new int[3];

    public ArrayStack(int size)

    {

        if( size > 3)

        {

            threeStacks = new int[size];

            int capacity = size/3;

            _min[0] = 0; _max[0] = capacity - 1;

            _min[1] = capacity; _max[1] = (capacity*2) -1;

            _min[2] = capacity*2; _max[2] = size-1;

            _pointer[0] = -1;

            _pointer[1] = capacity - 1;

            _pointer[2] = (capacity*2) -1;

        }

        else 

        {

            throw new Exception("Size is less than 3");

        }

    }

    public string Pop(int stackNumber)

    {

        stackNumber = actualStackNumber(stackNumber); 

​

            if(_pointer[stackNumber] < _min[stackNumber])

                return ("Stack is Empty");

​

            else

            {

                int answer = threeStacks[_pointer[stackNumber]];

                _pointer[stackNumber]--;

                return answer.ToString();

            }

    }

    public void Push(int stackNumber, int number)

    {

        stackNumber = actualStackNumber(stackNumber); 

        if(_pointer[stackNumber] == _max[stackNumber])

            Console.WriteLine("Stack is Full");

        else

        {

            _pointer[stackNumber]++;

            threeStacks[_pointer[stackNumber]] = number;

        }

    }

    public string Peek(int stackNumber)

    {

        stackNumber = actualStackNumber(stackNumber); 

        if(_pointer[stackNumber] < _min[stackNumber])

            return "Stack is Empty";

        else

        {

            int answer = threeStacks[_pointer[stackNumber]];

            return answer.ToString();

        }

    }

    public bool IsEmpty(int stackNumber)

    {

        return (_pointer[stackNumber] < _min[stackNumber]);

    }

    public bool IsFull(int stackNumber)

    {

        return (_pointer[stackNumber] == _max[stackNumber]);

    }

    private int actualStackNumber(int num)

    {

        if(num >3 || num < 1)

            throw new Exception("Wrong Stack Number");

        return (num-1);  

    }

}