C++ Multithreading code on Sort array CHATGPT

#include <iostream>
#include <thread>
#include <vector>
#include <algorithm>

void quicksort(std::vector<int>& arr, int left, int right) {
    if (left >= right) {
        return;
    }

    int pivot = arr[(left + right) / 2];
    int i = left;
    int j = right;

    while (i <= j) {
        while (arr[i] < pivot) {
            i++;
        }
        while (arr[j] > pivot) {
            j--;
        }
        if (i <= j) {
            std::swap(arr[i], arr[j]);
            i++;
            j--;
        }
    }

    std::thread t1(quicksort, std::ref(arr), left, j);
    std::thread t2(quicksort, std::ref(arr), i, right);

    t1.join();
    t2.join();
}

int main() {
    std::vector<int> arr = {9, 3, 7, 1, 5, 8, 2, 6, 4};

    quicksort(arr, 0, arr.size() - 1);

    std::cout << "Sorted array: ";
    for (int num : arr) {
        std::cout << num << " ";
    }
    std::cout << std::endl;

    return 0;
}