// Implement 2 stacks of integers on the base of integer array of fixed size. The total

// length of both stacks can be limited by the size of the array (e.g. it is OK to crash on

// attempt to push too many elements in total).

using System;

​

public class TwoStacks

{

    // stack 1 occupies first count1 elements of array with the bottom at data[0]

    // stack 2 occupies last count2 elements of array with the bottom at data[data.Length-1]

    int count1, count2;

    int[] data;

    public TwoStacks(int n)

    {

        data = new int[n];

        count1 = 0;

        count2 = 0;

    }

    public void Push1(int v)

    {

        AssertNotFull();

        data[count1] = v;

        count1++;

    }

    public void Push2(int v)

    {

        AssertNotFull();

        count2++;

        data[data.Length - count2] = v;

    }

    public int Pop1()

    {

        if (count1 <= 0)

           throw new ApplicationException("Stack1 underflow");

​

        count1--;

        return data[count1];

    }

    public int Pop2()

    {

        if (count2 <= 0)

           throw new ApplicationException("Stack2 underflow");

​

        int v = data[data.Length - count2];

        count2--;

        return v;

    }

    private void AssertNotFull()

    {

        if (count1 + count2 >= data.Length)

           throw new ApplicationException("Container is full");

    }

}

​

public class Program

{

    public static void Main(string[] args)

    {

        TwoStacks s = new TwoStacks(5);

        TestPush(s, 1, 5);

        TestPush(s, 2, 100);

        TestPush(s, 2, 67);

        TestPush(s, 1, 89);

        TestPush(s, 2, 9);

        TestPop (s, 1);

        TestPush(s, 2, 40);

        TestPop (s, 2);

    }

    private static void TestPush(TwoStacks s, int index, int v)

    {

        Console.WriteLine("Push{0}({1})", index, v);

        if(index==1)

            s.Push1(v);

        else if(index==2)

            s.Push2(v);

    }

​

    private static void TestPop(TwoStacks s, int index)

    {

        int v = -1;

        if(index==1)

            v = s.Pop1();

        else if(index==2)

            v = s.Pop2();

        Console.WriteLine("Pop{0} = {1}", index, v);

    }

}

​