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#!/usr/bin/perl -s
use v5.16;
use Test2::V0;
use warnings FATAL => 'all';
use Scalar::Util 'looks_like_number';
use experimental 'signatures';
our ($tests, $examples, $verbose);
run_tests() if $tests || $examples; # does not return
say(<<EOS), exit unless @ARGV;
usage: $0 [-examples] [-tests] [--] [string]
-examples
run the examples from the challenge
-tests
run some tests
-verbose
print diagnostic information
string
string to test if it represents a palindrome number
EOS
### Input and Output
my $ret = palindrome_number($ARGV[0]);
if ($verbose) {
say "got $ARGV[0]" if $verbose;
if (!defined $ret) {
say 'is not a number';
} else {
say "has value ", 0 + $ARGV[0];
if ($ret eq '') {
say 'reverse value is not a number';
} elsif ($ret) {
say "is palindrome";
} else {
say "is not palindrome";
}
}
}
say 0 + !!$ret;
### Implementation
# The concept of "number palindromes" needs further specifications to be
# well defined because "palindromic" is a string property and there is no
# unique string representation of a number. Following the examples I'll
# take the decimal representation of a number that has to form a palindrome.
# Though there seems to be some consensus on considering integer numbers
# only, *any* numeric value is allowed here.
#
# A string shall be considered as palindromic number, iff the
# transformation chain
# numify->stringify->reverse->numify->stringify
# resembles the input string. (All transformations from a Perl view.)
#
# This sub uses different false return values to signal the failed test:
# - undef for a non-numeric input string
# - the empty string for a non-numeric reversed numified input string
# - zero for a numeric forward and backward value that is not a palindrome
# number
sub palindrome_number ($str) {
return unless looks_like_number $str;
my $reverse = reverse $str + 0;
return '' unless looks_like_number $reverse;
0 + ($str eq $reverse + 0);
}
### Examples and tests
sub run_tests {
SKIP: {
skip "examples" unless $examples;
ok palindrome_number(1221), 'example 1: 1221 is palindrome';
ok !palindrome_number(-101), 'example 2: -101 is not palindrome';
ok !palindrome_number(90), 'example 3: 90 is not palindrome';
}
SKIP: {
skip "tests" unless $tests;
for my $str (qw(21e12 1.221e3 0012100 00121 0012.2100)) {
ok !palindrome_number($str), "$str is not palindrome";
}
for my $str (qw(12.21 1221)) {
ok palindrome_number($str), "$str is palindrome";
}
# specific return codes
is palindrome_number('1O2O1'), U(), 'not a number';
is palindrome_number('-101'), '', 'reverse not a number';
is palindrome_number('1e-21'), '', 'reverse not a number';
is palindrome_number('12327'), 0, 'not palindrome';
is palindrome_number('+121.0'), 0, 'not palindrome';
is palindrome_number('121'), 1, 'palindrome';
# exotic cases: NaN vs. nan
is palindrome_number('NaN'), 0, 'NaN is numeric';
is palindrome_number('nan'), 1, 'possibly the strangest case';
}
done_testing;
exit;
}
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