Two Sum: Sort&Search Solution

Problem Specs:

Solution(Implemented in C):

/**
 * Abstract:Sort the array(with qsort) and for every element a[i], search(with bsearch) 
 * target - a[i].
 * NOTE: An aux-array is allocated to preserve the original order so we can find the 
 * target pair's indices.
 */

int cmpfunc (const void * a, const void * b) {
   return ( *(int*)a - *(int*)b );
}

int find(int a[], int n, int t, int si) {
    for (int i = 0; i < n; i++) { if (i != si && a[i] == t) return i; }
    return -1;
}

int* twoSum(int* nums, int numsSize, int target, int* returnSize) {
    int *a = (int*)malloc(numsSize * sizeof(*a));
    for (int i = 0; i < numsSize; i++) { *(a + i) = *(nums + i); }
    qsort(a, numsSize, sizeof(*a), cmpfunc);

    int *r = NULL;
    for (int i = 0; i < numsSize; i++) {
        int key = target - a[i];
        int *item = (int*)bsearch(&key, a, numsSize, sizeof(*a), cmpfunc);
        if (item != NULL && item != a + i) { 
            r = (int*)malloc(2 * sizeof(*r));
            *r = i;
            *(r + 1) = item - a;
            break; 
        }
    }
    if (r != NULL) {
        int *ret = (int*)malloc(2 * sizeof(ret));
        *ret = find(nums, numsSize, a[*r], -1);
        *(ret + 1) = find(nums, numsSize, a[*(r + 1)], *ret);
        *returnSize = 2;
        return ret;
    }
    if (returnSize != NULL) { *returnSize = 0; }
    return NULL;
}