priority.cpp

/*
Title: Priority CPU Scheduling
Description: Non-preemptive priority scheduling with Gantt chart and time display.
Time Complexity: O(n²)
Space Complexity: O(n)
*/

#include <iostream>
#include <vector>
#include <climits>
using namespace std;

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

void printGanttChart(const vector<int> &gantt, const vector<int> &time) {
    cout << "\nGantt Chart:\n ";
    for (int pid : gantt)
        cout << "|  P" << pid << "  ";
    cout << "|\n";
    cout << time[0];
    for (int i = 1; i < (int)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;
        cout << "Priority (Lower number = Higher priority): ";
        cin >> p[i].priority;
    }

    vector<int> wt(n), tat(n), gantt, time(1, 0);
    vector<bool> done(n, false);
    int completed = 0, t = 0;
    float totalWT = 0, totalTAT = 0;

    while (completed < n) {
        int idx = -1, minP = INT_MAX;
        for (int i = 0; i < n; i++) {
            if (!done[i] && p[i].at <= t && p[i].priority < minP) {
                minP = p[i].priority;
                idx = i;
            }
        }

        if (idx == -1) {
            t++;
            continue;
        }

        gantt.push_back(p[idx].pid);
        t += p[idx].bt;
        time.push_back(t);
        tat[idx] = t - p[idx].at;
        wt[idx] = tat[idx] - p[idx].bt;
        done[idx] = true;
        completed++;
    }

    cout << "\n--- Priority Scheduling ---\n";
    cout << "PID\tAT\tBT\tPRIO\tWT\tTAT\n";
    for (int i = 0; i < n; i++) {
        cout << "P" << p[i].pid << "\t" << p[i].at << "\t" << p[i].bt
             << "\t" << p[i].priority << "\t" << wt[i] << "\t" << tat[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;
}