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/* 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>
#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(void)
{
// randomly generate some numbers
int *arr = new int[TEST_SIZE];
for (size_t i = 0; i < TEST_SIZE; ++i)
{
arr[i] = rand() % (2L << 30);
}
printf("Before: ");
print_arr(arr, TEST_SIZE);
printf("\n");
quicksort(arr, TEST_SIZE);
printf("After: ");
print_arr(arr, TEST_SIZE);
printf("\n");
delete[] arr;
return 0;
}
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