LIFO (Last-In-First-Out) approach in Programming

Last Updated : 01 Sep, 2022

Prerequisites - FIFO (First-In-First-Out) approach in Programming, FIFO vs LIFO approach in Programming
LIFO is an abbreviation for last in, first out. It is a method for handling data structures where the first element is processed last and the last element is processed first.

Real-life example:

In this example, following things are to be considered:

There is a bucket that holds balls.
Different types of balls are entered into the bucket.
The ball to enter the bucket last will be taken out first.
The ball entering the bucket next to last will be taken out after the ball above it (the newer one).
In this way, the ball entering the bucket first will leave the bucket last.
Therefore, the Last ball (Blue) to enter the bucket gets removed first and the First ball (Red) to enter the bucket gets removed last.

This is known as Last-In-First-Out approach or LIFO.

Where is LIFO used:

Data Structures:
Certain data structures like Stacks and other variants of Stacks use LIFO approach for processing data.
Extracting latest information:
Sometimes computers use LIFO when data is extracted from an array or data buffer. When it is required to get the most recent information entered, the LIFO approach is used.

Program Examples for LIFO:

Implementation: Using Stack data structure.

C++

// C++ program to demonstrate 
// working of LIFO 
// using stack in C++ 
#include<bits/stdc++.h>
using namespace std;

// Pushing element on the top of the stack 
stack<int> stack_push(stack<int> stack) 
{ 
    for (int i = 0; i < 5; i++) 
    { 
        stack.push(i); 
    } 
    return stack;
} 

// Popping element from the top of the stack 
stack<int> stack_pop(stack<int> stack) 
{ 
    cout << "Pop :"; 

    for (int i = 0; i < 5; i++) 
    { 
        int y = (int)stack.top();
        stack.pop();
        cout << (y) << endl; 
    } 
    return stack;
} 

// Displaying element on the top of the stack 
void stack_peek(stack<int> stack) 
{ 
    int element = (int)stack.top(); 
    cout << "Element on stack top : " << element << endl; 
} 

// Searching element in the stack 
void stack_search(stack<int> stack, int element) 
{ 
    int pos = -1,co = 0;
    while(stack.size() > 0)
    {
        co++;
        if(stack.top() == element)
        {
            pos = co;
            break;
        }
        stack.pop();
    }

    if (pos == -1) 
        cout << "Element not found" << endl; 
    else
        cout << "Element is found at position " << pos << endl; 
} 

// Driver code
int main() 
{ 
    stack<int> stack ; 

    stack = stack_push(stack); 
    stack = stack_pop(stack); 
    stack = stack_push(stack); 
    stack_peek(stack); 
    stack_search(stack, 2); 
    stack_search(stack, 6); 
    return 0;
}
    
// This code is contributed by Arnab Kundu

Java

// Java program to demonstrate
// working of LIFO
// using Stack in Java

import java.io.*;
import java.util.*;

class GFG {
    // Pushing element on the top of the stack
    static void stack_push(Stack<Integer> stack)
    {
        for (int i = 0; i < 5; i++) {
            stack.push(i);
        }
    }

    // Popping element from the top of the stack
    static void stack_pop(Stack<Integer> stack)
    {
        System.out.println("Pop :");

        for (int i = 0; i < 5; i++) {
            Integer y = (Integer)stack.pop();
            System.out.println(y);
        }
    }

    // Displaying element on the top of the stack
    static void stack_peek(Stack<Integer> stack)
    {
        Integer element = (Integer)stack.peek();
        System.out.println("Element on stack top : " + element);
    }

    // Searching element in the stack
    static void stack_search(Stack<Integer> stack, int element)
    {
        Integer pos = (Integer)stack.search(element);

        if (pos == -1)
            System.out.println("Element not found");
        else
            System.out.println("Element is found at position " + pos);
    }

    public static void main(String[] args)
    {
        Stack<Integer> stack = new Stack<Integer>();

        stack_push(stack);
        stack_pop(stack);
        stack_push(stack);
        stack_peek(stack);
        stack_search(stack, 2);
        stack_search(stack, 6);
    }
}

Python3

# Python3 program to demonstrate working of LIFO

# Pushing element on the top of the stack
def stack_push(stack):
    for i in range(5):
        stack.append(i)
    return stack
 
# Popping element from the top of the stack
def stack_pop(stack):
    print("Pop :")
 
    for i in range(5):
        y = stack[-1]
        stack.pop()
        print(y)
    return stack
 
# Displaying element on the top of the stack
def stack_peek(stack):
    element = stack[-1]
    print("Element on stack top :", element)
 
# Searching element in the stack
def stack_search(stack, element):
    pos = -1
    co = 0
    while(len(stack) > 0):
        co+=1
        if(stack[-1] == element):
            pos = co
            break
        stack.pop()
 
    if (pos == -1):
        print( "Element not found")
    else:
        print("Element is found at position", pos)

stack = []
stack_push(stack)
stack_pop(stack)
stack_push(stack)
stack_peek(stack)
stack_search(stack, 2)
stack_search(stack, 6)

# This code is contributed by rameshtravel07.

// C# program to demonstrate 
// working of LIFO 
// using Stack in C# 
using System;
using System.Collections.Generic;

class GFG
{ 
    // Pushing element on the top of the stack 
    static void stack_push(Stack<int> stack) 
    { 
        for (int i = 0; i < 5; i++)
        { 
            stack.Push(i); 
        } 
    } 

    // Popping element from the top of the stack 
    static void stack_pop(Stack<int> stack) 
    { 
        Console.WriteLine("Pop :"); 

        for (int i = 0; i < 5; i++)
        { 
            int y = (int)stack.Pop(); 
            Console.WriteLine(y); 
        } 
    } 

    // Displaying element on the top of the stack 
    static void stack_peek(Stack<int> stack) 
    { 
        int element = (int)stack.Peek(); 
        Console.WriteLine("Element on stack top : " + element); 
    } 

    // Searching element in the stack 
    static void stack_search(Stack<int> stack, int element) 
    { 
        bool pos = stack.Contains(element); 

        if (pos == false) 
            Console.WriteLine("Element not found"); 
        else
            Console.WriteLine("Element is found at position " + pos); 
    } 

    // Driver code
    public static void Main(String[] args) 
    { 
        Stack<int> stack = new Stack<int>(); 

        stack_push(stack); 
        stack_pop(stack); 
        stack_push(stack); 
        stack_peek(stack); 
        stack_search(stack, 2); 
        stack_search(stack, 6); 
    } 
} 

// This code contributed by Rajput-Ji

JavaScript

<script>

// JavaScript program to demonstrate 
// working of LIFO 


// Pushing element on the top of the stack 
function stack_push(stack) 
{ 
    for (var i = 0; i < 5; i++) 
    { 
        stack.push(i); 
    } 
    return stack;
} 

// Popping element from the top of the stack 
function stack_pop(stack) 
{ 
    document.write(  "Pop :<br>"); 

    for (var i = 0; i < 5; i++) 
    { 
        var y = parseInt(stack[stack.length-1]);
        stack.pop();
        document.write( y + "<br>"); 
    } 
    return stack;
} 

// Displaying element on the top of the stack 
function stack_peek(stack) 
{ 
    var element = parseInt(stack[stack.length-1]); 
    document.write( "Element on stack top : " + element + 
    "<br>"); 
} 

// Searching element in the stack 
function stack_search( stack,  element) 
{ 
    var pos = -1,co = 0;
    while(stack.length > 0)
    {
        co++;
        if(stack[stack.length-1] == element)
        {
            pos = co;
            break;
        }
        stack.pop();
    }

    if (pos == -1) 
        document.write( "Element not found" + "<br>"); 
    else
        document.write("Element is found at position " 
        + pos + "<br>"); 
} 

    stack=[] ; 

    stack = stack_push(stack); 
    stack = stack_pop(stack); 
    stack = stack_push(stack); 
    stack_peek(stack); 
    stack_search(stack, 2); 
    stack_search(stack, 6); 

    
// This code is contributed by SoumikMondal

</script>

Output

Pop :4
3
2
1
0
Element on stack top : 4
Element is found at position 3
Element not found

Complexity Analysis:

Time Complexity: O(n)
Auxiliary Space: O(n)

LIFO (Last-In-First-Out) approach in Programming

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