fcfs.cpp

/*
Title: First Come First Serve (FCFS) CPU Scheduling
Description: Implements FCFS scheduling using arrival and burst times with Gantt chart and time display.
Time Complexity: O(n log n) (for sorting)
Space Complexity: O(n)
*/

#include <bits/stdc++.h>
using namespace std;

struct Process {
    int pid, at, bt;
};

// Sort by Arrival Time
bool compareArrival(Process &a, Process &b) {
    return a.at < b.at;
}

// Print Gantt Chart
void printGanttChart(vector<int> &gantt, vector<int> &time) {
    cout << "\nGantt Chart:\n";
    for (int pid : gantt)
        cout << "|  P" << pid << "  ";
    cout << "|\n";

    for (int i = 0; i < time.size(); i++)
        cout << time[i] << "      " ;
    cout << "\n";
}

int main() {
    int n;
    cout << "Enter number of processes: ";
    cin >> n;

    vector<Process> p(n);
    for (int i = 0; i < n; i++) {
        p[i].pid = i + 1;
        cout << "\nEnter details for Process " << i + 1 << "\n";
        cout << "Arrival Time: ";
        cin >> p[i].at;
        cout << "Burst Time: ";
        cin >> p[i].bt;
    }

    sort(p.begin(), p.end(), compareArrival);

    vector<int> wt(n), tat(n), ct(n);
    vector<int> gantt, time;
    float totalWT = 0, totalTAT = 0;

    int current = max(0, p[0].at);
    time.push_back(current);

    for (int i = 0; i < n; i++) {
        current = max(current, p[i].at);
        current += p[i].bt;
        ct[i] = current;
        tat[i] = ct[i] - p[i].at;
        wt[i] = tat[i] - p[i].bt;
        gantt.push_back(p[i].pid);
        time.push_back(ct[i]);
    }

    cout << "\n--- First Come First Serve (FCFS) ---\n";
    cout << "PID\tAT\tBT\tCT\tTAT\tWT\n";
    for (int i = 0; i < n; i++) {
        cout << "P" << p[i].pid << "\t" << p[i].at << "\t" << p[i].bt << "\t"<<ct[i]<<"\t"
             << tat[i] << "\t" << wt[i] << "\n";
        totalWT += wt[i];
        totalTAT += tat[i];
    }

    cout << "Average Waiting Time = " << totalWT / n << "\n";
    cout << "Average Turnaround Time = " << totalTAT / n << "\n";
    printGanttChart(gantt, time);
    return 0;
}