Guest Check-In

You get two arrays of names, invited and arrived. Return how many invited guests haven't arrived yet.

A guest may check in more than once. They still count as one guest.

Someone who wasn't invited may check in too. They don't change the answer.

Example 1:

Input: invited = ["Ava", "Leo", "Mia", "Zoe"], arrived = ["Leo", "Zoe"]
Output: 2
Explanation: Leo and Zoe are here.
Ava and Mia haven't arrived yet.

Example 2:

Input: invited = ["Ava", "Leo"], arrived = ["Leo", "Max", "Leo"]
Output: 1
Explanation: Leo checked in twice, but he is one guest.
Max wasn't invited.
Only Ava is missing.

Example 3:

Input: invited = ["Sam", "Kim"], arrived = []
Output: 2
Explanation: Nobody has arrived yet.

Constraints:

• invited has 1 to 100 names.
• arrived has 0 to 100 names.
• The names in invited are all different.
• Each name is one word of English letters, starting with a capital letter.