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// Calculate sum of n numbers using Pthreads. A list of n numbers is divided into two smaller  list of equal size, two separate threads are used to sum the sub lists.

#include <pthread.h>
#include <iostream>
#include <vector>
using namespace std;

// Structure to pass data to threads
struct ThreadData {
    vector<int>& arr;
    int start;
    int end;
    int sum;
};

// Thread function to calculate the sum of a sublist
void* calculate_sum(void* arg) {
    ThreadData* data = static_cast<ThreadData*>(arg);
    data->sum = 0;
    for (int i = data->start; i < data->end; ++i) {
        data->sum += data->arr[i];
    }
    pthread_exit(nullptr);
}

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

    vector<int> arr(n);
    cout << "Enter " << n << " elements: " << endl;
    for (int i = 0; i < n; ++i) {
        cin >> arr[i];
    }

    // Split the list into two halves
    int mid = n / 2;
    
    // Create thread data structures
    ThreadData data1 = {arr, 0, mid, 0};
    ThreadData data2 = {arr, mid, n, 0};

    pthread_t thread1, thread2;

    // Create two threads
    pthread_create(&thread1, nullptr, calculate_sum, static_cast<void*>(&data1));
    pthread_create(&thread2, nullptr, calculate_sum, static_cast<void*>(&data2));

    // Wait for both threads to finish
    pthread_join(thread1, nullptr);
    pthread_join(thread2, nullptr);

    // Calculate the total sum
    int total_sum = data1.sum + data2.sum;

    cout << "The sum of the numbers is: " << total_sum << endl;

    return 0;
}