GFG_ImplementTwoStacksInArray.cpp

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

// { Driver Code Starts
#include<bits/stdc++.h>

using namespace std;

class twoStacks
{
    int *arr;
    int size;
    int top1, top2;
public:
   twoStacks(int n=100){size = n; arr = new int[n]; top1 = -1; top2 = size;}
 
   void push1(int x);
   void push2(int x);
   int pop1();
   int pop2();
};



int main()
{

    int T;
    cin>>T;
    while(T--)
    {
        twoStacks *sq = new twoStacks();

        int Q;
        cin>>Q;
        while(Q--){
        int stack_no;
        cin>>stack_no;
        int QueryType=0;
        cin>>QueryType;
        
        if(QueryType==1)
        {
            int a;
            cin>>a;
            if(stack_no ==1)
            sq->push1(a);
            else if(stack_no==2)
            sq->push2(a);
        }else if(QueryType==2){
        	if(stack_no==1)
            cout<<sq->pop1()<<" ";
            else if(stack_no==2)
            cout<<sq->pop2()<<" ";

        }
        }
        cout<<endl;
    }
}
// } Driver Code Ends





//Function to push an integer into the stack1.
void twoStacks :: push1(int x)
{
    if(top1 +1 == top2)
    {
        cout<<"Overflow"<<endl;
        return;
    }
    
    arr[++top1] = x;
}
   
//Function to push an integer into the stack2.
void twoStacks ::push2(int x)
{
    if(top1 +1 == top2)
    {
        cout<<"Overflow"<<endl;
        return;
    }
    arr[--top2] = x;
}
   
//Function to remove an element from top of the stack1.
int twoStacks ::pop1()
{
    if(top1 == -1)
        return -1;
    return arr[top1--];
    
}

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