/* qsort.cpp
 * Date: 2024-06-22
 * Author: Aryadev Chavali
 * Commentary: The inplace O(nlog(n)) sortitng algorithm.  Originally designed
 * in C, hence the lack of iostream.
 */
#include <cstdio>
#include <cstdlib>
#include <fstream>
#include <iostream>
#include <vector>

#define ARR_SIZE(XS) (sizeof(XS) / sizeof((XS)[0]))
#define SWAP(A, B) \
  do               \
  {                \
    (A) ^= (B);    \
    (B) ^= (A);    \
    (A) ^= (B);    \
  } while (0)

void print_arr(int *arr, int size)
{
  printf("{\n");
  for (int i = 0; i < size; ++i)
    printf("  %d,\n", arr[i]);
  printf("}\n");
}

void quicksort(int *arr, int arr_size)
{
  // TODO: Use a different sort for small enough sizes?
  if (arr_size > 1)
  {
    // TODO: Choose a better pivot maybe?
    int pivot       = arr[arr_size - 1]; // Choose the last element as pivot
    int pivot_index = -1;

    for (int j = 0; j < arr_size; ++j)
    {
      if (arr[j] < pivot)
      {
        ++pivot_index;
        std::swap(arr[pivot_index], arr[j]);
      }
    }

    std::swap(arr[pivot_index + 1], arr[arr_size - 1]);

    // TODO: Use a stack here instead?
    quicksort(arr, pivot_index + 1);
    quicksort(arr + pivot_index + 1, arr_size - pivot_index - 1);
  }
}

int main(int argc, char *argv[])
{
  (void)argc;
  (void)argv;

#define TEST_SIZE 10
  // randomly generate some numbers
  int *arr     = new int[TEST_SIZE];
  int arr_size = TEST_SIZE;

  for (size_t i = 0; i < TEST_SIZE; ++i)
    arr[i] = rand() % (2L << 30);

  // Use nums.txt
  // std::ifstream input(argc > 1 ? argv[1] : "nums.txt");
  // std::vector<int> num_vec;

  // for (std::string line; std::getline(input, line);
  //      num_vec.push_back(std::stoi(line)))
  //   continue;
  // int *arr = &num_vec[0];
  // int arr_size = num_vec.size();

  printf("Before: ");
  print_arr(arr, arr_size);
  printf("\n");

  quicksort(arr, arr_size);

  printf("After: ");
  print_arr(arr, arr_size);
  printf("\n");

  delete[] arr;

  return 0;
}