Implement_two_stacks_in_an_array.java

// { Driver Code Starts
import java.util.*;

class TwoStack {

  int size;
  int top1, top2;
  // int arr[] = new int[size];
  int arr[] = new int[100];

  TwoStack() {
    int n = 100;
    size = n;
    // arr[] = new int[n];
    top1 = -1;
    top2 = size;
  }

  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    int T = sc.nextInt();
    while (T > 0) {
      TwoStack sq = new TwoStack();

      int Q = sc.nextInt();
      while (Q > 0) {
        int stack_no = sc.nextInt();
        int QueryType = sc.nextInt();

        Stacks g = new Stacks();

        if (QueryType == 1) {
          int a = sc.nextInt();
          if (stack_no == 1)
            g.push1(a, sq);
          else if (stack_no == 2)
            g.push2(a, sq);
        } else if (QueryType == 2) {
          if (stack_no == 1)
            System.out.print(g.pop1(sq) + " ");
          else if (stack_no == 2)
            System.out.print(g.pop2(sq) + " ");
        }

        Q--;
      }
      System.out.println();
      T--;
    }
  }
}

// } Driver Code Ends

/*
 * Structure of the class is
 * class TwoStack
 * {
 * 
 * int size;
 * int top1,top2;
 * int arr[] = new int[100];
 * 
 * TwoStack()
 * {
 * size = 100;
 * top1 = -1;
 * top2 = size;
 * }
 * }
 */

class Stacks {
  void push1(int x, TwoStack sq) {
    sq.arr[++sq.top1] = x;
  }

  // Function to push an integer into the stack2.
  void push2(int x, TwoStack sq) {
    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++];
  }
}