Certainty should be adjusted to a problem, there is no simple answer. For this Kata's task even 1 is enough as it should pass tests only once and won't be used anymore.

Okay I found it, we have to use completing the square...thanks

Approved.

lol that image

PHP translation kumited.

Done.

Already added a similar fixed test to all languages in the sample and final tests.

Add a test case which is cap = 100,on = 50,wait = 40.
The value return should be 0.

Added a fixed test, now this solution is invalid.

What if the cap = 100,on = 50,wait = 40?
The number return will be -10.
It supposed to return 0 as Kata Description said.

Any explanation or related topic to be shared for searching?

Any explanation why this is the best practice?

agree with you. Why everyone is keep upvoting? The community in codewar seems not that alert with extreme cases.