void insertionSort(int arr[], int len) {
    for (int i = 1; i < len; i++) {
        int key = arr[i];
        int j = i - 1;
        while ((j >= 0) && (key < arr[j])) {
            arr[j + 1] = arr[j];
            j--;
        }
        arr[j + 1] = key;
    }
}