perl solution for challenge 74 task 2

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+#!/usr/bin/env perl
+use strict;
+use warnings;
+use feature qw(:5.32);
+use experimental qw(signatures);
+
+# TASK #2 › FNR Character
+# Submitted by: Mohammad S Anwar
+#
+# You are given a string $S.
+#
+# Write a script to print the series of first non-repeating character
+# (left -> right) for the given string. Print # if none found.
+#
+# Example 1
+# Input: $S = ‘ababc’
+# Output: ‘abb#c’
+# Pass 1: “a”, the FNR character is ‘a’
+# Pass 2: “ab”, the FNR character is ‘b’
+# Pass 3: “aba”, the FNR character is ‘b’
+# Pass 4: “abab”, no FNR found, hence ‘#’
+# Pass 5: “ababc” the FNR character is ‘c’
+#
+# Example 2
+# Input: $S = ‘xyzzyx’
+# Output: ‘xyzyx#’
+# Pass 1: “x”, the FNR character is “x”
+# Pass 2: “xy”, the FNR character is “y”
+# Pass 3: “xyz”, the FNR character is “z”
+# Pass 4: “xyzz”, the FNR character is “y”
+# Pass 5: “xyzzy”, the FNR character is “x”
+# Pass 6: “xyzzyx”, no FNR found, hence ‘#’
+
+my $s = $ARGV[0];
+my @c = split //, $s;
+my %seen;
+my @nr;
+my @out;
+
+for my $c (@c) {
+    # have we seen $c before?
+    unless (defined $seen{$c}) {
+        # add $c to @nr
+        $seen{$c} = 1;
+        push @nr, $c;
+    } else {
+        # remove $c from @nr
+        for my $i (0..$#nr) {
+            if ($nr[$i] eq $c) {
+                splice @nr, $i, 1;
+                last;
+            }
+        }
+    }
+
+    # now the FNR is either the last element of @nr, or #
+    push @out, @nr ? $nr[-1] : '#';
+}
+
+say join '', @out;