#include <stdio.h>

struct process {
    int pid;
    int burst_time;
    int remaining_time;
};

int find_shortest_process(struct process p[], int n, int current_time) {
    int i, shortest_index = -1, shortest_time = 9999;

    for(i=0; i<n; i++) {
        if(p[i].remaining_time > 0 && p[i].burst_time < shortest_time && current_time >= p[i].arrival_time) {
            shortest_time = p[i].burst_time;
            shortest_index = i;
        }
    }

    return shortest_index;
}

void sjf_preemptive(struct process p[], int n) {
    int i, current_time = 0, total_time = 0, completed = 0;
    float avg_wait_time = 0, avg_turnaround_time = 0;

    printf("\nGantt Chart:\n");

    while(completed != n) {
        int shortest_index = find_shortest_process(p, n, current_time);

        if(shortest_index == -1) {
            current_time++;
            continue;
        }

        p[shortest_index].remaining_time--;

        printf("%d P%d ", current_time, p[shortest_index].pid);

        if(p[shortest_index].remaining_time == 0) {
            completed++;
            total_time = current_time+1;
            printf("%d\n", total_time);
            avg_wait_time += total_time - p[shortest_index].burst_time - p[shortest_index].arrival_time;
            avg_turnaround_time += total_time - p[shortest_index].arrival_time;
        }

        current_time++;
    }

    avg_wait_time /= n;
    avg_turnaround_time /= n;

    printf("\nAverage Waiting Time: %.2f", avg_wait_time);
    printf("\nAverage Turnaround Time: %.2f", avg_turnaround_time);
}

int main() {
    int n, i;
    printf("Enter the number of processes: ");
    scanf("%d", &n);

    struct process p[n];

    for(i=0; i<n; i++) {
        printf("\nEnter the arrival time and burst time for process %d: ", i+1);
        scanf("%d %d", &p[i].arrival_time, &p[i].burst_time);
        p[i].pid = i+1;
        p[i].remaining_time = p[i].burst_time;
    }

    sjf_preemptive(p, n);

    return 0;
}