TL;DR

Here we are with TASK #1 from The Weekly Challenge #189. Enjoy!

The challenge

You are given an array of characters (a..z) and a target character.

Write a script to find out the smallest character in the given array lexicographically greater than the target character.

Example 1

Input: @array = qw/e m u g/, $target = 'b'
Output: e

Example 2

Input: @array = qw/d c e f/, $target = 'a'
Output: c

Example 3

Input: @array = qw/j a r/, $target = 'o'
Output: r

Example 4

Input: @array = qw/d c a f/, $target = 'a'
Output: c

Example 5

Input: @array = qw/t g a l/, $target = 'v'
Output: v

The questions

Can we assume that the target character is one of the ones inside the a..z range?

The solution

We will sweep the whole array in search for the character that is both greater than the target and minimum.

Well, not necessarily the whole array, because if we hit the character immediately following the character, we’re not going to find anything lower, so we can just stop looking for something different.

Raku:

#!/usr/bin/env raku
use v6;
sub MAIN ($target, *@array) { put greater-character(@array, $target) }

sub greater-character (@array, $target) {
   (my $after-target = $target)++;
   my $retval = Nil;
   for @array -> $char {
      next unless $char gt $target;
      $retval = $char if !defined($retval) || $char le $retval;
      last if $retval eq $after-target;
   }
   return $retval;
}

Perl:

#!/usr/bin/env perl
use v5.24;
use warnings;
use experimental 'signatures';
no warnings 'experimental::signatures';

my $target = shift;
say greater_character([@ARGV], $target);

sub greater_character ($array, $target) {
   (my $after_target = $target)++;
   my $retval = undef;
   for my $char ($array->@*) {
      next unless $char gt $target;
      $retval //= $char;
      $retval = $char if !defined($retval) || $char le $retval;
      last if $retval eq $after_target;
   }
   return $retval;
}

We might also return Nil/undef if the target character is z, right?

Stay safe!