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#!/usr/bin/env perl
# https://theweeklychallenge.org/blog/perl-weekly-challenge-329/#TASK2
#
# Task 2: Nice String
# ===================
#
# You are given a string made up of lower and upper case English letters only.
#
# Write a script to return the longest substring of the give string which is
# nice. A string is nice if, for every letter of the alphabet that the string
# contains, it appears both in uppercase and lowercase.
#
## Example 1
##
## Input: $str = "YaaAho"
## Output: "aaA"
#
#
## Example 2
##
## Input: $str = "cC"
## Output: "cC"
#
#
## Example 3
##
## Input: $str = "A"
## Output: ""
##
## No nice string found.
#
############################################################
##
## discussion
##
############################################################
#
# For each character in $str, we use the lowercase character of it
# as the key in a hash. There we keep track of each character that
# we have seen so far whether it was in lower, upper or both cases.
# In the end, we walk the characters from $str again and just keep
# the ones for which we have seen both the lower and upper case
# variant.
use v5.36;
nice_string("YaaAho");
nice_string("cC");
nice_string("A");
sub nice_string($str) {
say "Input: \"$str\"";
my @chars = split //, $str;
my $seen = {};
my $result = "";
foreach my $char (@chars) {
if($char =~ m/[a-z]/) {
$seen->{$char}->{lc} = 1;
} else {
$seen->{lc($char)}->{uc} = 1;
}
}
foreach my $char (@chars) {
if($seen->{lc($char)}->{lc} && $seen->{lc($char)}->{uc}) {
$result .= $char;
}
}
say "Output: \"$result\"";
}
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