## C, sort, odd_even_sort.c

``````/**
* @file
* @author [Edwin Ajong](https://github.com/eddybruv)
* @brief [Odd Even Sort](https://en.wikipedia.org/wiki/Odd%E2%80%93even_sort) implementation
* @details
* This algorithm is divided into two phases- Odd and Even Phase.
* The algorithm runs until the array elements are sorted and in each iteration two phases occurs- Odd and Even Phases.
* In the odd phase, we perform a bubble sort on odd indexed elements and in the even phase,
* we perform a bubble sort on even indexed elements.
* Time Complexity: O(N ^ 2)
*/

#include <assert.h>     /// for assert
#include <stdbool.h>    /// for bool
#include <stdio.h>      /// for IO operations
#include <stdlib.h>     /// for dynammic memory allocation
#include <time.h>       /// for random number generation
#include <inttypes.h>   /// for int32_t types

/**
* @brief Swap numbers by reference(using pointers)
* @param first pointer to first number
* @param second pointer to second number
* @returns void
*/
void swap(int32_t *first, int32_t *second)
{
int32_t temp = *first;
*first = *second;
*second = temp;
}

/**
* @brief oddEvenSort sorts the array using the algorithm described above.
* @details
* A boolean varaible(isSorted) is declared and initialised to "false".
* In the while loop, the variable(isSorted) is then set to "true".
* During even phase the for loop loops through the array, touching just the even indexes.
* i.e arr[0], arr[2], arr[4] and so on.
* While during the odd phase, the for loop loops through the array, touching just the odd indexes.
* i.e arr[1], arr[3], arr[5] and so on.
* During these phases, if the if statement check if the interger at the current position in the array
* is greater than the interger at the next array index (i.e arr[index + 2], to make sure the index is odd
* during the odd phase and even during the even phase).
* If the condition is true, the function "swap" is called and address of the intergers in question are passed as
* parameters. After the swap is completed, "isSorted" is set to "false".
* The while loop will keep running till the array is propertly sorted.
* @param arr array to be sorted
* @param size the size of the array
* @returns void
*/
void oddEvenSort(int *arr, int size)
{
bool isSorted = false;
while(!isSorted)
{
isSorted = true;
int32_t i;

// Even phase
for(i = 0; i <= size - 2; i += 2)
{
if(arr[i] > arr[i + 1])
{
swap(&arr[i], &arr[i + 1]);
isSorted = false;
}
}

// Odd phase
for(i = 1; i <= size - 2; i += 2)
{
if(arr[i] > arr[i + 1])
{
swap(&arr[i], &arr[i + 1]);
isSorted = false;
}
}
}
}

/**
* @brief Self-test implementations
* @details Two tests (unsorted) arrays were created and their corresponding solution(sorted) arrays were also created.
* The test arrays and their respective sizes are then passed in to the oddEvenSort function.
* To test if the algorithm works, a for loop is assigned to loop through the both arrays(test and solution) and check if the array elements
* of the test array correspond to the elements of the solution array.
* @returns void
*/
static void test()
{
int32_t arr1[] = {-9, 2, 3, 1};
int32_t arr1Soln[] = {-9, 1, 2, 3};
int32_t arr2[] = {9, 7, 5, 3, 8, 2, 1, 4, 0, 6};
int32_t arr2Soln[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

oddEvenSort(arr1, 4);
oddEvenSort(arr2, 10);

for (int32_t i = 0; i < 4; i++)
{
assert(arr1[i] == arr1Soln[i]);
}

for (int32_t i = 0; i < 10; i++)
{
assert(arr2[i] == arr2Soln[i]);
}
printf("All tests have passed!\n");
}

/**
* @brief Main function
* @returns 0 on exit
*/
int main()
{
test();  // run self-test implementations
return 0;
}
``````