Updating secondary list

[TheClusk]

Hello everyone, fairly new to Sharepoint, i just wondered if i could pick all your brains!
I have developed a simple 'Holiday Request' PowerApp which populates data into a sharepoint list.

i need this sharepoint list to 'talk' to another, and update it

we have about 60 members of staff and only 7 are allowed off at the same time

so...

>the first sharepoint list will have staff members holiday request dates on it.

>The second list will have a column full of dates. And the number "7" in the next column (for the number of spaces we have, to have off).

i need this number 7 to reduce by 1, everytime someone requests holiday on that day, from the other list.

is this doable?
I was going to make the second list of dates a sharepoint calendar instead. But i don't know how doable that is

[#2]

@TheClusk I can think of 2 ways to do achieve this:

1. Add a data source of 2nd list to your Power Apps. Find the unique item from 2nd list for which you are adding holiday request in 1st list. Then update the item in 2nd list with new number using Patch function 

2. Run Power Automate flow on item creation (& maybe on item update) in 1st list. Find the unique item from 2nd list for which you are adding holiday request in 1st list. Then update the item in 2nd list with new number using Update item action in Power automate.

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[#3]

Thank you for your reply

Only probelm i have is that List 1 has...

holiday request date from (12th may) & to (19th may) (not a list of each seperate day)

list 2 will have that list of seperate days. (12th, 13th,14th,15th etc...)

How would i get around this?