TwoStacksInOneArray.java

/*https://practice.geeksforgeeks.org/problems/implement-two-stacks-in-an-array/1*/

class Stacks
{
    //Function to push an integer into the stack1.
    void push1(int x, TwoStack sq)
    {
        ++sq.top1;
        if (sq.top1 == sq.top2)
        {
        	--sq.top1;
            return;
        }
        sq.arr[sq.top1] = x;
    }

    //Function to push an integer into the stack2.
    void push2(int x, TwoStack sq)
    {
        --sq.top2;
        if (sq.top1 == sq.top2)
        {
        	++sq.top2;
            return;
        }
        sq.arr[sq.top2] = x;
    }

    //Function to remove an element from top of the stack1.
    int pop1(TwoStack sq)
    {
        if (sq.top1 == -1) return -1;
        return sq.arr[sq.top1--];
    }

    //Function to remove an element from top of the stack2.
    int pop2(TwoStack sq)
    {
        if (sq.top2 == sq.size) return -1;
        return sq.arr[sq.top2++];
    }
}