set_difference.c

#include <stdio.h>
#include <stdlib.h>
struct Array
{

    int A[10];
    int size;
    int length;
};

void Display(struct Array arr)
{
    for (int i = 0; i < arr.length; i++)
        printf("%d ", arr.A[i]);
}

struct Array *Difference(struct Array *arr1, struct Array *arr2)
{
    int i = 0, j = 0, k = 0;
    struct Array *arr3 = (struct Array *)malloc(sizeof(struct Array));
    while (i < arr1->length && j < arr2->length)
    {
        if (arr1->A[i] < arr2->A[j])
            arr3->A[k++] = arr1->A[i++];
        else if (arr2->A[j] < arr1->A[i])
            j++;
        else
        {
            i++;
            j++;
        }
    }

    for (; arr1->length; i++)
        arr3->A[k++] = arr1->A[i];

    arr3->length = k;
    arr3->size = 10;

    return arr3;
}

int main()
{
    struct Array arr1 = {{2, 6, 10, 15, 25}, 10, 5};
    struct Array arr2 = {{3, 6, 7, 15, 20}, 10, 5};
    struct Array *arr3;

    arr3 = Difference(&arr1, &arr2);
    Display(*arr3);
    return 0;
}

// Output
// 6 15
// O(n)