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FIFO (First-In-First-Out) approach in Programming

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  • Difficulty Level : Basic
  • Last Updated : 21 Jun, 2022

FIFO is an abbreviation for first in, first out. It is a method for handling data structures where the first element is processed first and the newest element is processed last.
Real life example:
 

In this example, following things are to be considered: 
 

  • There is a ticket counter where people come, take tickets and go.
  • People enter a line (queue) to get to the Ticket Counter in an organized manner.
  • The person to enter the queue first, will get the ticket first and leave the queue.
  • The person entering the queue next will get the ticket after the person in front of him
  • In this way, the person entering the queue last will the tickets last
  • Therefore, the First person to enter the queue gets the ticket first and the Last person to enter the queue gets the ticket last.

This is known as First-In-First-Out approach or FIFO.
Where is FIFO used:
 

  1. Data Structures
    Certain data structures like Queue and other variants of Queue uses FIFO approach for processing data. 
     
  2. Disk scheduling
    Disk controllers can use the FIFO as a disk scheduling algorithm to determine the order in which to service disk I/O requests. 
     
  3. Communications and networking
    Communication network bridges, switches and routers used in computer networks use FIFOs to hold data packets en route to their next destination.

Program Examples for FIFO
Program 1: Queue 
 

C++




// C++ program to demonstrate
// working of FIFO
// using Queue interface in C++
 
#include<bits/stdc++.h>
using namespace std;
 
// print the elements of queue
void print_queue(queue<int> q)
{
    while (!q.empty())
    {
        cout << q.front() << " ";
        q.pop();
    }
    cout << endl;
}
 
// Driver code
int main()
{
    queue<int> q ;
 
    // Adds elements {0, 1, 2, 3, 4} to queue
    for (int i = 0; i < 5; i++)
        q.push(i);
 
    // Display contents of the queue.
    cout << "Elements of queue-";
         
    print_queue(q);
 
    // To remove the head of queue.
    // In this the oldest element '0' will be removed
    int removedele = q.front();
    q.pop();
    cout << "removed element-" << removedele << endl;
 
    print_queue(q);
 
    // To view the head of queue
    int head = q.front();
    cout << "head of queue-" << head << endl;
 
    // Rest all methods of collection interface,
    // Like size and contains can be used with this
    // implementation.
    int size = q.size();
    cout << "Size of queue-" << size;
         
    return 0;
}
 
// This code is contributed by Arnab Kundu


Java




// Java program to demonstrate
// working of FIFO
// using Queue interface in Java
 
import java.util.LinkedList;
import java.util.Queue;
 
public class QueueExample {
    public static void main(String[] args)
    {
        Queue<Integer> q = new LinkedList<>();
 
        // Adds elements {0, 1, 2, 3, 4} to queue
        for (int i = 0; i < 5; i++)
            q.add(i);
 
        // Display contents of the queue.
        System.out.println("Elements of queue-" + q);
 
        // To remove the head of queue.
        // In this the oldest element '0' will be removed
        int removedele = q.remove();
        System.out.println("removed element-" + removedele);
 
        System.out.println(q);
 
        // To view the head of queue
        int head = q.peek();
        System.out.println("head of queue-" + head);
 
        // Rest all methods of collection interface,
        // Like size and contains can be used with this
        // implementation.
        int size = q.size();
        System.out.println("Size of queue-" + size);
    }
}


Python3




# Python program to demonstrate
# working of FIFO
# using Queue interface in Java
 
q = []
 
# Adds elements {0, 1, 2, 3, 4} to queue
for i in range(5):
    q.append(i)
 
# Display contents of the queue.
print("Elements of queue-" , q)
 
# To remove the head of queue.
# In this the oldest element '0' will be removed
removedele = q.pop(0)
print("removed element-" , removedele)
 
print(q)
 
# To view the head of queue
head = q[0]
print("head of queue-" , head)
 
# Rest all methods of collection interface,
# Like size and contains can be used with this
# implementation.
size = len(q)
print("Size of queue-" , size)
 
# This code is contributed by patel2127.


C#




// C# program to demonstrate
// working of FIFO
using System;
using System.Collections.Generic;
 
public class QueueExample
{
    public static void Main(String[] args)
    {
        Queue<int> q = new Queue<int>();
 
        // Adds elements {0, 1, 2, 3, 4} to queue
        for (int i = 0; i < 5; i++)
            q.Enqueue(i);
 
        // Display contents of the queue.
        Console.Write("Elements of queue-");
        foreach(int s in q)
                Console.Write(s + " ");
 
        // To remove the head of queue.
        // In this the oldest element '0' will be removed
        int removedele = q.Dequeue();
        Console.Write("\nremoved element-" + removedele + "\n");
        foreach(int s in q)
                Console.Write(s + " ");
 
        // To view the head of queue
        int head = q.Peek();
        Console.Write("\nhead of queue-" + head);
 
        // Rest all methods of collection interface,
        // Like size and contains can be used with this
        // implementation.
        int size = q.Count;
        Console.WriteLine("\nSize of queue-" + size);
    }
}
 
// This code has been contributed by 29AjayKumar


Javascript




<script>
 
// JavaScript program to demonstrate
// working of FIFO
// using Queue interface in Java
 
let q = [];
// Adds elements {0, 1, 2, 3, 4} to queue
for (let i = 0; i < 5; i++)
    q.push(i);
 
// Display contents of the queue.
document.write("Elements of queue-[" + q.join(", ")+"]<br>");
 
// To remove the head of queue.
// In this the oldest element '0' will be removed
let removedele = q.shift();
document.write("removed element-" + removedele+"<br>");
 
document.write("["+q.join(", ")+"]<br>");
 
// To view the head of queue
let head = q[0];
document.write("head of queue-" + head+"<br>");
 
// Rest all methods of collection interface,
// Like size and contains can be used with this
// implementation.
let size = q.length;
document.write("Size of queue-" + size+"<br>");
 
 
// This code is contributed by avanitrachhadiya2155
 
</script>


Output:  

Elements of queue-[0, 1, 2, 3, 4]
removed element-0
[1, 2, 3, 4]
head of queue-1
Size of queue-4

Time Complexity: O(N)
Space Complexity: O(N)
 


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