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#!/usr/bin/perl -s
use v5.16;
use Test2::V0;
use bigint;
use Coro::Generator;
our ($tests, $examples);
run_tests() if $tests || $examples; # does not return
die <<EOS unless @ARGV;
usage: $0 [-examples] [-tests] [N]
-examples
run the examples from the challenge
-tests
run some tests
N
Print the first N left factorials.
EOS
### Input and Output
main: {
my $left_factorial = gen_left_factorial();
say $left_factorial->() for 1 .. $ARGV[0];
}
### Implementation
# Build a generator for left factorials
sub gen_left_factorial {
my ($index, $factorial, $left_factorial) = (0, 1, 1);
generator {
yield $left_factorial;
yield $left_factorial += ($factorial *= ++$index) while 1;
}
}
### Examples and tests
sub run_tests {
SKIP: {
skip "examples" unless $examples;
my $left_factorial = gen_left_factorial();
is [map $left_factorial->(), 1 .. 10],
[1, 2, 4, 10, 34, 154, 874, 5914, 46234, 409114], 'task 1';
}
SKIP: {
skip "tests" unless $tests;
my $left_factorial = gen_left_factorial();
$left_factorial->() for 1 .. 21;
is $left_factorial->(), 53652269665821260314, 'from OEIS';
}
done_testing;
exit;
}
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