RogerBW's Blog

The Weekly Challenge 309: All You Minima 23 February 2025

I’ve been doing the Weekly Challenges. The latest involved various list analyses. (Note that this ends today.)

Task 1: Min Gap

You are given an array of integers, @ints, increasing order.

Write a script to return the element before which you find the smallest gap.

So we look at each pair, and store the lowest. There are functional approaches to this but I tend to stick to the straightforward one, and the code looks basically the same across all the languages I'm using. Crystal:

def mingap(a)

The initial "smallest difference" is the last value minus the first.

  mg = a[-1] - a[0]
  mv = 0

Look at each pair.

  a.each_cons(2) do |p|

Work out the difference.

    delta = p[1] - p[0]

If it's smaller than previously seen, store the second value.

    if delta < mg
      mg = delta
      mv = p[1]
    end
  end
  mv
end

Task 2: Min Diff

You are given an array of integers, @ints.

Write a script to find the minimum difference between any two elements.

Obviously one could do this with a combination generator, but I don't usually bother when it's just two loops.

Raku:

sub mindiff(@a) {

This time I don't have an initialising "smallest difference" value, so I use $n as a flag to indicate that we haven't yet had a value.

    my $md = 0;
    my $n = False;

As before, loop and calculate differences.

    for 0 .. @a.end - 1 -> $i {
        for $i + 1 .. @a.end -> $j {
            my $diff = abs(@a[$i] - @a[$j]);

If I haven't seen a value yet, or this value is lower than the previous best, store it.

            if (!$n || $diff < $md) {
                $md = $diff;
                $n = True;
            }
        }
    }
    $md;
}

Full code on github.

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