The weekly challenge 329 - Task 2: Nice String

 1 #!/usr/bin/env perl
 2 # https://theweeklychallenge.org/blog/perl-weekly-challenge-329/#TASK2
 3 #
 4 # Task 2: Nice String
 5 # ===================
 6 #
 7 # You are given a string made up of lower and upper case English letters only.
 8 #
 9 # Write a script to return the longest substring of the give string which is
10 # nice. A string is nice if, for every letter of the alphabet that the string
11 # contains, it appears both in uppercase and lowercase.
12 #
13 ## Example 1
14 ##
15 ## Input: $str = "YaaAho"
16 ## Output: "aaA"
17 #
18 #
19 ## Example 2
20 ##
21 ## Input: $str = "cC"
22 ## Output: "cC"
23 #
24 #
25 ## Example 3
26 ##
27 ## Input: $str = "A"
28 ## Output: ""
29 ##
30 ## No nice string found.
31 #
32 ############################################################
33 ##
34 ## discussion
35 ##
36 ############################################################
37 #
38 # For each character in $str, we use the lowercase character of it
39 # as the key in a hash. There we keep track of each character that
40 # we have seen so far whether it was in lower, upper or both cases.
41 # In the end, we walk the characters from $str again and just keep
42 # the ones for which we have seen both the lower and upper case
43 # variant.
44 
45 use v5.36;
46 
47 nice_string("YaaAho");
48 nice_string("cC");
49 nice_string("A");
50 
51 sub nice_string($str) {
52     say "Input: \"$str\"";
53     my @chars = split //, $str;
54     my $seen = {};
55     my $result = "";
56     foreach my $char (@chars) {
57         if($char =~ m/[a-z]/) {
58             $seen->{$char}->{lc} = 1;
59         } else {
60             $seen->{lc($char)}->{uc} = 1;
61         }
62     }
63     foreach my $char (@chars) {
64         if($seen->{lc($char)}->{lc} && $seen->{lc($char)}->{uc}) {
65             $result .= $char;
66         }
67     }
68     say "Output: \"$result\"";
69 }
70