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#!/usr/bin/env perl
# vim:set ts=4 sw=4 sts=4 et ai wm=0 nu:
#=============================================================================
# Perl Weekly Challenge Week 196, Challenge 1
#=============================================================================
# Copyright (c) 2022, Bob Lied
#=============================================================================
# You are given a list of integers, @list.
# Write a script to find out subsequence that respect Pattern 132.
# Return empty array if none found.
# Pattern 132 in a sequence (a[i], a[j], a[k])
# such that i < j < k and a[i] < a[k] < a[j].
# Example 1 Input: @list = (3, 1, 4, 2)
# Output: (1, 4, 2) respect the Pattern 132.
# Example 2 Input: @list = (1, 2, 3, 4)
# Output: () since no susbsequence can be found.
# Example 3 Input: @list = (1, 3, 2, 4, 6, 5)
# Output: (1, 3, 2) more than one subsequence found, return first.
# Example 4 Input: @list = (1, 3, 4, 2)
# Output: (1, 3, 2)
#
#=============================================================================
use v5.36;
use List::Util qw/first/;
use List::MoreUtils qw/after_incl/;
use Getopt::Long;
my $Verbose = 0;
my $DoTest = 0;
GetOptions("test" => \$DoTest, "verbose" => \$Verbose);
exit(!runTest()) if $DoTest;
my @list = @ARGV;
my $answer = find132(\@list);
say "(", join(", ", $answer->@*), ")";
exit 0;
sub is132($list, $i1, $i2, $i3)
{
return $list->[$i1] < $list->[$i2]
&& $list->[$i1] < $list->[$i3]
&& $list->[$i2] < $list->[$i3];
}
sub find132($list)
{
return [] if scalar(@$list) < 3;
while ( my $first = shift @$list )
{
my @tail = after_incl { $_ > $first } $list->@*;
while ( my $middle = shift @tail )
{
my $last = first { $_ > $first && $_ < $middle } @tail;
if ( $last )
{
return [ $first, $middle, $last ];
}
}
}
return [];
}
sub runTest
{
use Test2::V0;
is( find132( [ 3,2,1,0 ] ), [ ], "Descending");
is( find132( [ 1,3,2 ] ), [1,3,2], "Obvious");
is( find132( [ 3,1,4,2 ] ), [1,4,2], "Example 1");
is( find132( [ 1,2,3,4 ] ), [ ], "Example 2");
is( find132( [ 1,3,2,4,6,5 ] ), [1,3,2], "Example 3");
is( find132( [ 1,3,4,2 ] ), [1,3,2], "Example 4");
done_testing;
}
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