RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved splitting sentences and processing arrays. (Note that this ends today.)

Task 1: Max Words

You are given a list of sentences, @list.

A sentence is a list of words that are separated by a single space with no leading or trailing spaces.

Write a script to find out the maximum number of words that appear in a single sentence.

Not having to account for multiple, leading, or trailing spaces makes this much easier than it might be. Broadly I used two approaches depending on which was easier in each language: counting the spaces (then adding 1), as in Lua:

function maxwords(a)
   local m = 0
   for i, v in ipairs(a) do
      local ct = 0
      for n, m in string.gmatch(v, "%s") do
         ct = ct + 1
      end
      if ct > m then
         m = ct
      end
   end
   return m + 1
end

or splitting the string, as in Javascript:

function maxwords(a) {
    return Math.max(...a.map(x => x.split(" ").length));
}

Task 2: Left Right Sum Diff

You are given an array of integers, @ints.

Write a script to return left right sum diff array as shown below:

(I.e. for a sequence [a..e], produce a sequence [-(c+d+e), a-(d+e), (a+b)-(e), (a+b+c)] - taking the absolute value of each term.)

My basic approach is in two stages: build up the list of sums (from front and back), then produce the differences.

In Raku:

sub leftrightsumdiff(@a) {
    my $al = @a.end;

@left is 0, a, a+b, etc.; @right is 0, e, e+d, etc.

    my @left = [0];
    my @right = [0];
    for 0 .. $al-1 -> $i {
        @left.push(@left[$i] + @a[$i]);
        @right.push(@right[$i] + @a[$al - $i]);
    }

I reverse @right and combine the two.

    return Array(zip(@left, @right.reverse).map({abs($_[0] - $_[1])}));
}

Basically every modern language seems to have something like zip for iterating two arrays in parallel. The exceptions were Perl, Lua, PostScript and JavaScript, for which I used an explicit index. (Probably I should add one to my PostScript libraries, though I haven't often needed it outside these problems.)

Full code on github.