Sudo Placement[1.3] | Stack Design

Given q number of queries, you need to perform operations on the stack. Queries are of three types 1, 2 and 3. If the operation is to push (1) then push the elements, if the operations is to pop (2) then pop the element and if it is Top (3), then print the element at the top of stack (If stack is empty, print “-1”, without quotes).

Examples:

Input: Queries =  6
                  3
                  1 5
                  1 6
                  1 7
                  2
                  3
Output: -1
         6 
The first query is to print top, but since the stack is empty, so we print -1.
Next three queries are to push 5, 6, and 7, so we pushed them on a stack. 
Next query is pop, so we popped 7 from a stack. Final query is to print the
top, so 6 is there at the top and thus printed.

Approach: Stack can be used to perform the given operation. If the input for a query is 1, then take another input and push the element into the stack using push() function. If the input for a query is 2, then pop the element using pop() function in a stack. If the input for a query is 3, then print the top element using top() function.



Below is the implemenatation of the above aprpoach:

C++

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// C++ program for
// Sudo-Placement | Stack Design
#include <bits/stdc++.h>
using namespace std;
  
stack<int> s;
  
// function to perform type-1 operation
void _push(int n)
{
    s.push(n);
}
  
// function to perform type-2 operation
void _pop()
{
    s.pop();
}
  
// function to perform type-3 operation
void print()
{
    // if the stack is not empty
    if (!s.empty())
        cout << s.top() << endl;
    else
        cout << -1 << endl;
}
  
// Driver Code
int main()
{
    // 1st query
    print();
    // 2nd query
    _push(5);
  
    // 3rd query
    _push(6);
  
    // 4th query
    _push(7);
  
    // 5th query
    _pop();
  
    // 6th query
    print();
  
    return 0;
}

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Java

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import java.util.*;
// Java program for
// Sudo-Placement | Stack Design
  
class GFG 
{
  
    static Stack<Integer> s = new Stack<>();
  
    // function to perform type-1 operation
    static void _push(int n) 
    {
        s.push(n);
    }
  
    // function to perform type-2 operation
    static void _pop() 
    {
        s.pop();
    }
  
    // function to perform type-3 operation
    static void print() 
    {
          
        // if the stack is not empty
        if (!s.empty()) 
        {
            System.out.println(s.peek());
        
        else 
        {
            System.out.println(-1);
        }
    }
  
    // Driver Code
    public static void main(String[] args) 
    {
        // 1st query
        print();
        // 2nd query
        _push(5);
  
        // 3rd query
        _push(6);
  
        // 4th query
        _push(7);
  
        // 5th query
        _pop();
  
        // 6th query
        print();
    }
}
  
// This code contributed by Rajput-Ji

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C#

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// C# program for
// Sudo-Placement | Stack Design
using System;
using System.Collections.Generic;
  
class GFG 
{
  
    static Stack<int> s = new Stack<int>();
  
    // function to perform type-1 operation
    static void _push(int n) 
    {
        s.Push(n);
    }
  
    // function to perform type-2 operation
    static void _pop() 
    {
        s.Pop();
    }
  
    // function to perform type-3 operation
    static void print() 
    {
          
        // if the stack is not empty
        if (s.Count != 0) 
        {
            Console.WriteLine(s.Peek());
        
        else
        {
            Console.WriteLine(-1);
        }
    }
  
    // Driver Code
    public static void Main() 
    {
        // 1st query
        print();
        // 2nd query
        _push(5);
  
        // 3rd query
        _push(6);
  
        // 4th query
        _push(7);
  
        // 5th query
        _pop();
  
        // 6th query
        print();
    }
}
  
/* This code contributed by PrinciRaj1992 */

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Output:

-1
6


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Improved By : Rajput-Ji, princiraj1992



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