Sort_ArrayOf_012s.c

#include <stdio.h>

/* Function to swap *a and *b */
void swap(int* a, int* b);

// Sort the input array, the array is assumed to
// have values in {0, 1, 2}
void sort012(int a[], int arr_size)
{
    int lowerLimit = 0;
    int upperLimit = arr_size - 1;
    int mid = 0;
    // Iterate till all the elements
    // are sorted
    while (mid <= upperLimit) {
        switch (a[mid]) {
            // If the element is 0
        case 0:
            swap(&a[lowerLimit++], &a[mid++]);
            break;
            // If the element is 1
        case 1:
            mid++;
            break;
            // If the element is 2
        case 2:
            swap(&a[mid], &a[upperLimit--]);
            break;
        }
    }
}

/* UTILITY FUNCTIONS */
void swap(int* a, int* b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}

/* Utility function to print array arr[] */
void printArray(int arr[], int arr_size)
{
    int i;
    for (i = 0; i < arr_size; i++)
        printf("%d ", arr[i]);
}

/* driver program to test */
int main()
{
    int arr[] = { 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 };
    int arr_size = sizeof(arr) / sizeof(arr[0]);
    int i;

    sort012(arr, arr_size);

    printArray(arr, arr_size);

    getchar();
    return 0;
}