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Sudo Placement[1.3] | Stack Design
  • Difficulty Level : Basic
  • Last Updated : 02 Nov, 2020

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 are to pop (2) then pop the element and if it is Top (3), then print the element at the top of the stack (If the 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 the push() function. If the input for a query is 2, then pop the element using the pop() function in a stack. If the input for a query is 3, then print the top element using the top() function. 
Below is the implementation of the above approach: 
 

C++




// 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;
}

Java




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

Python3




# Python3 program for
# Sudo-Placement | Stack Design
s = [];
 
# function to perform
# type-1 operation
def _push(n):
    s.append(n);
 
# function to perform
# type-2 operation
def _pop():
    s.pop();
 
# function to perform
# type-3 operation
def _print():
 
    # if the stack is not
    # empty
    if (len(s) > 0):
        print(s[len(s) - 1]);
    else:
        print("-1");
 
# Driver Code
if __name__ == '__main__':
   
    # 1st query
    _print();
     
    # 2nd query
    _push(5);
 
    # 3rd query
    _push(6);
 
    # 4th query
    _push(7);
 
    # 5th query
    _pop();
 
    # 6th query
    _print();
 
# This code is contributed by 29AjayKumar

C#




// 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 */
Output: 
-1
6



 

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