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| -rw-r--r-- | challenge-074/jo-37/perl/ch-2.pl | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/challenge-074/jo-37/perl/ch-2.pl b/challenge-074/jo-37/perl/ch-2.pl new file mode 100644 index 0000000000..8cbc7ae0b9 --- /dev/null +++ b/challenge-074/jo-37/perl/ch-2.pl @@ -0,0 +1,53 @@ +#!/usr/bin/perl + +use v5.16; +use Test2::V0; +use warnings FATAL => 'all'; + +use List::Util qw(first); + +# The description of the task and the given examples are - to my +# understanding - not consistent. +# +# "Write a script to print the series of first non-repeating character +# (left -> right) for the given string." +# +# Input: $S = 'ababc' +# Output: 'abb#c' +# Pass 1: "a", the FNR character is 'a' +# Pass 2: "ab", the FNR character is 'b' +# +# The characters chosen in the examples are apparently the "first +# non-repeating character (right -> left). I'd rather call this +# the "last non-repeating" character (LNR). +# +# Maybe this little ambiguity is intentional. At least it adds a nice +# new aspect. So this sub provides both variants. + +sub nr_char { + my @arr = split //, shift; + # mode: fnr or lnr + my $lnr = shift; + my (%freq, @head); + + join '', map { + # While traversing the input string character-wise, + # count frequencies and collect the (reversed) head. + $freq{$_}++; + + # Emulate unshift (lnr, reversed) or push (fnr, forward) + # to augment the head. + splice @head, $lnr ? 0 : @head, 0, $_; + + # The first singleton character from the (reversed) head + # is the requested output character. + (first {$freq{$_} == 1} @head) // '#'; + } @arr; +} + +is nr_char('ababc', 1), 'abb#c', 'first example, lnr'; +is nr_char('xyzzyx', 1), 'xyzyx#', 'second example, lnr'; +is nr_char('ababc'), 'aab#c', 'first example, fnr'; +is nr_char('xyzzyx'), 'xxxxx#', 'second example, fnr'; + +done_testing; |