#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

#define MAX_THREADS 4

// Shared data
int *arr;
long long partial_sum[MAX_THREADS];
int n;

// Per-thread input
typedef struct {
    int thread_id;
    int start;
    int end;
} thread_data;

void *compute_sum(void *args) {
    thread_data *data = (thread_data *)args;
    long long sum = 0;

    for (int i = data->start; i < data->end; i++)
        sum += arr[i];

    partial_sum[data->thread_id] = sum;
    pthread_exit(NULL);
}

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

    arr = (int *)malloc(n * sizeof(int));
    printf("Enter %d elements:\n", n);
    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    pthread_t threads[MAX_THREADS];
    thread_data threadArgs[MAX_THREADS];

    int chunk = n / MAX_THREADS;

    // Create threads
    for (int i = 0; i < MAX_THREADS; i++) {
        threadArgs[i].thread_id = i;
        threadArgs[i].start = i * chunk;

        // last thread takes the remaining elements
        threadArgs[i].end = (i == MAX_THREADS - 1) ? n : (i + 1) * chunk;

        pthread_create(&threads[i], NULL, compute_sum, &threadArgs[i]);
    }

    // Wait for all threads
    for (int i = 0; i < MAX_THREADS; i++)
        pthread_join(threads[i], NULL);

    // Combine results
    long long total = 0;
    for (int i = 0; i < MAX_THREADS; i++)
        total += partial_sum[i];

    printf("Parallel sum = %lld\n", total);

    free(arr);
    return 0;
}