Feed order

topics holds the topics of the posts to put on a feed. topics[i] is the topic of post i. You arrange all the posts in a line, each exactly once, so that no two neighboring posts have the same topic.

Complete the function solution, which returns the number of such orders. Posts with the same topic are still different posts, so swapping two posts with the same topic gives a different order.

Function

solution(topics)

Constraints

• The length of topics is from 1 to 7.
• Each topic is a string of lowercase English letters, with a length from 1 to 10.

Examples

Starter code

def solution(topics):
    answer = 0
    return answer