I'm surprised that thid was got approved because mine seems to be duplicated.

When I was thinking about writing this kata I couldn't find any similar kata.

I'm not sure y this one got approved, but it looks very similar to this (I'm also not sure why I did not think about this kata being a dup back then, && even gave it a green vote ughhh...... )

It should be infinite, in other words - endless, limitless, illimitable, unending, unceasing, perpetual.
So never ending but within a time limit (12 seconds).

This is a new kind of task - you need to optimize server side code ^_^

The description doesn't say that there may be recursive callbacks.
It's better if you note it there.

Becase I wrote a piece of code that calls the fourth argument in the beginning, therefore causing "Maximum call stack size exceeded" error.

The same solution as Xom9lk's is and unrelated as well but I still like it ^_^

I'm not arguing with your solutions, it tricked me in the first glance, so notice for everyone else:

Such function only applies caching to a current call.
It means if the function takes 7 seconds to complete, calling it 3 times, in total, will take 21 seconds.

Reasonable. Added.

Mmm... Yeah, you're right. Fixed the headings, description and the conflict.

I suggest an additional test for a scenario where the template contains no # characters:

(112, "+( )") => "+( )"

IMHO this line in description:

You don't need to worry about validating numbers, they always have appropriate form.

conflicts with the lines that follow:

if there are digits in a number that can't be formated, they should be skipped.

if there are less digits than needed, should return "Invalid phone number"

It states that I don't have to validate numbers, and then goes on talking how to deal with numbers that don't fit the pattern, which essentially is a validation logic.

It's also confusing to me what does "digits in a number that can't be formated" mean and how one is supposed to skip them.

I suggest rewriting the description as follows:

You're given phone number and template by which it should be formated.

• If there are more digits than needed, they should be ignored.
• If there are less digits than needed, return "Invalid phone number".

Also, the title "Introduction" doesn't make sense when it's followed by the whole description of the problem.

The initial object should be affected too, as it's said in the description

Do you still need it?

Even though I fixed it

I see