RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved string intersections and serial XOR. (Note that this ends today.)

Task 1: Count Common

You are given two array of strings, @str1 and @str2.

Write a script to return the count of common strings in both arrays.

So basically a set intersection.

And some languages don't have sets, but everything I'm using at least has hashes/dicts/maps/associative arrays.

Raku:

sub countcommon(@a, @b) {
  my %aa = set(@a);
  my %bb = set(@b);
  (%aa (&) %bb).elems;
}

PostScript (with no local variables, though some of the functions I'm including do use them):

/countcommon {
    toset exch toset set.intersection length
} bind def

Task 2: Decode XOR

You are given an encoded array and an initial integer.

Write a script to find the original array that produced the given encoded array. It was encoded such that encoded[i] = orig[i] XOR orig[i + 1].

First output is the initial value, then xor with each in turn. Even Lua isn't particularly verbose here:

function decodexor(a, init)
   local out = { init }
   for _, v in ipairs(a) do
      table.insert(out, out[#out] ~ v)
   end
   return out
end

and in PostScript, not only no local variables needed, but all done with language primitives.

/decodexor {
    [ exch
      3 -1 roll
      {
          exch dup 3 -1 roll xor
      } forall
    ]
} bind def

Full code on github.