chit4

//C++ program for FIFO algorithm
#include <bits/stdc++.h>
using namespace std;

// Method to determine pager faults using FIFO
int getPageFaults(int pages[], int n, int frames)
{
// To denote the current page set, we use an unordered_set.
// It will help to have a quick check
// The availability of the page in the set.

unordered_set <int> set;
// The code will store the pages in FIFO technique
queue <int> indexes;

// Stating from the first page
int countPageFaults = 0;

for (int i=0; i < n; i++)
{
    // Checking the capacity to hold more pages
    if (set.size() < frames)
    {
        // if the page is absent, insert it into the set
        // the condition represents page fault
        if (set.find(pages[i])==set.end())
        {
            set.insert(pages[i]);
            // increment the conter for page fault
            countPageFaults++;
        
            // Push the current page into the queue
            indexes.push(pages[i]);
        }
    }

// If the queue is full, we need to remove one page through FIFO
// The topmost page from the queue will be removed
// Now insert the current page to meet the demand
    else
    {
        // Check if the page in demand is not already present in the queue
        if (set.find(pages[i]) == set.end())
        {
            // Remove the first page from the queue
            int val = indexes.front();
            indexes.pop();
            
            // Pop the index page
            set.erase(val);
            
            // Push the current page in the queue
            set.insert(pages[i]);
            indexes.push(pages[i]);
            
            // Increment page faults
            countPageFaults++;
        }
    }
}

return countPageFaults;

}

// Driver code
int main()
{
int pages[] = {4, 1, 2, 4, 5};
int n = sizeof(pages)/sizeof(pages[0]);
int frames = 4;

cout << "Page Faults: " << getPageFaults(pages, n, frames);

return 0;

}