Question

Given an array such as [10,42,45,45,61,61,75,90,1240], how do I find what numbers X is in between? For example, if X = 59, the answers would be [45,45,61,61].

It seems like the select enumerator would be perfect for this, but I can’t figure out how to select all of the elements on either side.

Answer 1

You seem to need the repeated values of the boundaries, don’t you? here is a functional approach just as an example. It’s O(n), so as pointed out by others you better use a O(log(n)) bisection algorithm if you have big input arrays (note: the value to check must be between xs.min and xs.max):

xs = [10,42,45,45,61,61,75,90,1240]
chk_pairs = xs.chunk { |x| x }.each_cons(2)
boundaries = chk_pairs.detect { |_, (y, ys)| y > 59 }.flat_map { |x, xs| xs }
#=> [45, 45, 61, 61]