int partition(vector<int>& arr, int low, int high) {
  
    // Choose the pivot
    int pivot = arr[high];
    int i = low - 1;

    // Traverse arr[;ow..high] and move all smaller
    
    for (int j = low; j <= high - 1; j++) {
        if (arr[j] < pivot) {
            i++;
            swap(arr[i], arr[j]);
        }
    }
    
    // Move pivot after smaller elements and return its posn
    swap(arr[i + 1], arr[high]);  
    return i + 1;
}

void quickSort(vector<int>& arr, int low, int high) {
  
    if (low < high) {
      
        // pi is the partition return index of pivot
        int pi = partition(arr, low, high);
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}