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#!/usr/bin/perl -s
use v5.16;
use Test2::V0 '!float';
use PDL;
use PDL::NiceSlice;
our ($tests, $examples);
run_tests() if $tests || $examples; # does not return
die <<EOS unless @ARGV > 1;
usage: $0 [-examples] [-tests] [--] [N1 N2...]
-examples
run the examples from the challenge
-tests
run some tests
N1 N2...
List of numbers
EOS
### Input and Output
say 0 + is_monotonic(@ARGV);
### Implementation
# Comparing consecutive elements from the list yields values in the set
# {-1, 0, 1}, where a non-monotonic list has both -1 and 1 in the result
# set. Summating over the absolute values of the unique results from
# the comparisons thus reveals the monotonic property: The sum will be
# two for a non-monotonic list.
sub is_monotonic {
my $list = pdl @_;
($list(1:-1) <=> $list(0:-2))->uniq->abs->sum < 2;
}
### Examples and tests
sub run_tests {
SKIP: {
skip "examples" unless $examples;
ok is_monotonic(1, 2, 2, 3), 'example 1';
ok !is_monotonic(1, 3, 2), 'example 2';
ok is_monotonic(6, 5, 5, 4), 'example 3';
}
SKIP: {
skip "tests" unless $tests;
}
done_testing;
exit;
}
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