PWC221 - Good Strings


Here we are with TASK #1 from The Weekly Challenge #221. Enjoy!

The challenge

You are given a list of @words and a string $chars.

A string is good if it can be formed by characters from $chars, each character can be used only once.

Write a script to return the sum of lengths of all good strings in words.

Example 1

Input: @words = ("cat", "bt", "hat", "tree")
       $chars = "atach"
Output: 6

The good strings that can be formed are "cat" and "hat" so the answer
is 3 + 3 = 6.

Example 2

Input: @words = ("hello", "world", "challenge")
       $chars = "welldonehopper"
Output: 10

The strings that can be formed are "hello" and "world" so the answer >     is 5 + 5 = 10.

The questions

Given past challenges, one question is whether characters case matters or not. Additional questions would be:

  • how should we handle accented characters?
  • special characters, like quotation marks, hyphens, dots, etc.

The solution

The Bag data structure fits perfectly, allowing us to check the inclusion via the aptly named operator:

#!/usr/bin/env raku
use v6;
sub MAIN (*@words is copy) {
   my $chars = @words.shift;
   say good-strings($chars, @words);

sub good-strings ($chars, @words) {
   my $cbag = $chars.comb.Bag;
   return @words.grep({ .comb.Bag ⊆ $cbag })».chars.sum;

There’s no such thing in Perl, so we will leverage hashes to do the checks.

#!/usr/bin/env perl
use v5.24;
use warnings;
use experimental 'signatures';

say good_strings(@ARGV);

sub good_strings ($chars, @words) {
   my %available;
   $available{$_}++ for split m{}mxs, $chars;
   my $retval = 0;
   for my $word (@words) {
      my %residual;
      for my $c (split m{}mxs, $word) {
         $residual{$c} //= $available{$c} // 0;
         next WORD if --$residual{$c} < 0;
      $retval += length($word);
   return $retval;

Cheers and stay safe!

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