Reverse Nodes in k-Group

def reverseKGroup(next, values, k):
    # Read the values in list order.
    order = []
    node = 0
    while node != -1:
        order.append(values[node])
        node = next[node]
    # Reverse every full block of k; a shorter last block stays as it is.
    for start in range(0, len(order) - k + 1, k):
        order[start:start + k] = order[start:start + k][::-1]
    return order

def reverseKGroup(next, values, k):
    head = 0           # the list's head; changes after the first group
    prev_tail = -1     # last node of the groups already reversed
    group_start = 0
    while True:
        # Find the node right after this group, or stop if fewer than k remain.
        after, count = group_start, 0
        while after != -1 and count < k:
            after = next[after]
            count += 1
        if count < k:
            break
        # Turn the group's k links around. Its first node ends up last
        # and links to the node after the group.
        prev, node = after, group_start
        for _ in range(k):
            following = next[node]
            next[node] = prev
            prev, node = node, following
        # prev is the group's new first node: hang it after the previous group.
        if prev_tail == -1:
            head = prev
        else:
            next[prev_tail] = prev
        prev_tail = group_start
        group_start = after
    # Walk the relinked list from its head.
    result = []
    node = head
    while node != -1:
        result.append(values[node])
        node = next[node]
    return result