// insertion sort
void insertion_sort(int a[], int n) {
    for (int i = 1; i < n; i++) {
        int b = a[i], // insertion element
            j = i - 1;
        while (j >= 0 && b < a[j]) {
            a[j + 1] = a[j]; // shifting
            j--;
        }
        a[j + 1] = b;
    }
}