Question

I have an array of 52 different values that I can pass through a class to get a number in return.

$array = array("A","B","C","D"...);

Each value passed through the class gives a different number that can be either positive or negative.
The numbers are not equally distributed but are sorted in natural order.

E.g.

$myclass->calculate("A"); // 2.3
$myclass->calculate("B"); // 0.25
$myclass->calculate("C"); // -1.3
$myclass->calculate("D"); // -6

I want to get the last value that return a number >= 0.20 (in the example would be “B”).

This should be done in the minimum number of “class invocation” to avoid time wasting.

I thought something like: divide $array in 2 pieces and calculate the number I get, if it is >= 20, then split the last part of $array in other 2 smaller pieces and so on. But I don’t know if this would work.

How would you solve this?

Thanks in advance.

Answer 1

What you’re describing is called a binary search, but it won’t really work for this use case, because you aren’t searching for a known value. Rather, you’re searching for the value that is the lowest number >= 0.2 in a set where the exact value 0.2 may not exist (if it were guaranteed to exist, then you could do a binary search for 0.2, and then your letter would simply be n - 1; n != 0).

If your range is always A-Z, a simple linear search would definitely be the easiest method. The time savings on a data set of 26 elements for using a more efficient method is negligible (talking milliseconds here), compared to implementation time.

Edit: I see you actually mentioned 52 elements, not 26. My point is still the same, though. The number of elements would need to be in the tens of thousands or more for there to be any significant savings, unless you are performing this operation in a tight loop.