Week 176 task 2

3 files changed, 185 insertions, 0 deletions

diff --git a/challenge-176/bob-lied/perl/ch-2.pl b/challenge-176/bob-lied/perl/ch-2.pl
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+++ b/challenge-176/bob-lied/perl/ch-2.pl
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+#!/usr/bin/env perl
+# vim:set ts=4 sw=4 sts=4 et ai wm=0 nu:
+#=============================================================================
+# ch-2.pl Perl Weekly Challenge Task 2 Reversible Numbers
+#=============================================================================
+# Copyright (c) 2023, Bob Lied
+#=============================================================================
+# Write a script to find out all Reversible Numbers below 100.
+# A number is said to be a reversible if sum of the number and its
+# reverse had only odd digits.
+# For example,
+# 36 is reversible number as 36 + 63 = 99 i.e. all digits are odd.
+# 17 is not reversible as 17 + 71 = 88, none of the digits are odd.
+#=============================================================================
+
+use v5.36;
+
+use builtin qw/true false/;
+no warnings "experimental::builtin";
+
+# To be an odd number, it has to be the sum of an even and an odd number.
+# We're considering only two-digit numbers, so that means if the first digit
+# is odd, the second must be even, and vice versa.  Generate the possibilities.
+my @candidate = ( glob("{1,3,5,7,9}{0,2,4,6,8}"), glob("{2,4,6,8}{1,3,5,7,9}") );
+
+say join ",", sort { $a <=> $b }
+                grep { $_ < 100 && allOdd($_ + revNum($_)) } @candidate;
+
+# There are two fairly obvious ways of reversing the number.  We can treat
+# it as a string and reverse the digits, or we can do the math.  The string
+# operations are actually faster.
+sub revNum($n)
+{
+    (my $r = reverse("$n")) =~ s/^0+//;
+    return +($r);
+}
+
+# Checking that all digits are odd.  Again, two possibilities:  do the math
+# one digit at a time, or treat as a string and test each digit.
+sub allOdd($n)
+{
+    my $isOdd = true; # Doesn't handle 0, but 0 is not happening here.
+    while ( $n && $isOdd )
+    {
+        $isOdd &&= ( $n % 10 ) % 2;
+        $n = int($n / 10);
+    }
+    return $isOdd;
+}
+
+sub allOdd_str($n)
+{
+    use List::Util qw/all/;
+    return all { $_ % 2 } split("", $n);
+}
diff --git a/challenge-176/bob-lied/perl/rev.c b/challenge-176/bob-lied/perl/rev.c
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+++ b/challenge-176/bob-lied/perl/rev.c
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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <time.h>
+
+void reverse(char s[])
+{
+     int i, j;
+     char c;
+
+     for (i = 0, j = strlen(s)-1; i<j; i++, j--) {
+         c = s[i];
+         s[i] = s[j];
+         s[j] = c;
+     }
+}  
+
+int rev1(int n)
+{
+    int r = n % 10;
+    while ( (n = n / 10) != 0 )
+    {
+        r = r*10 + n % 10;
+    }
+    return r;
+}
+
+int rev2(int n)
+{
+    char s[16];
+    sprintf(s, "%d", n);
+    reverse(s);
+    return ( atoi(s) );
+}
+
+int main(int argc, char **argv)
+{
+    int r;
+
+    const int start = 123400000;
+    const int end   = 123500000;
+
+    clock_t begin = clock();
+    for ( int n = start; n <= end; n++ )
+    {
+        r = rev1(n);
+    }
+    clock_t finish = clock();
+    double t = (double)(finish - begin) / CLOCKS_PER_SEC;
+    printf("rev numeric %d %f\n", r, t);
+
+    begin = clock();
+    for ( int n = start; n <= end; n++ )
+    {
+        r = rev2(n);
+    }
+    finish = clock();
+    t = (double)(finish - begin) / CLOCKS_PER_SEC;
+    printf("rev string %d %f\n", r, t);
+}
diff --git a/challenge-176/bob-lied/perl/rev.pl b/challenge-176/bob-lied/perl/rev.pl
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+++ b/challenge-176/bob-lied/perl/rev.pl
@@ -0,0 +1,69 @@
+#!/usr/bin/env perl
+# vim:set ts=4 sw=4 sts=4 et ai wm=0 nu:
+#=============================================================================
+# rev.pl
+#=============================================================================
+# Copyright (c) 2023, Bob Lied
+#=============================================================================
+# We need to reverse a number (e.g, 632 -> 236).  Which is faster: doing
+# the math, or treating it as a string?
+#=============================================================================
+
+use v5.36;
+
+use Benchmark qw/cmpthese/;
+
+use Getopt::Long;
+my $DoBenchmark = 0;
+my $DoTest  = 0;
+
+GetOptions("test" => \$DoTest, "benchmark" => \$DoBenchmark);
+
+if ( $DoBenchmark )
+{
+    cmpthese(-5, {
+            numeric => sub {
+                rev1($_) for 123400 .. 124500;
+            },
+            string  => sub {
+                rev2($_) for 123400 .. 124500;
+            },
+            }
+        );
+}
+exit(!runTest()) if $DoTest;
+
+sub rev1($n)
+{
+    use integer;
+    my $r = $n % 10;
+    while ( $n = int($n/10)  )
+    {
+        $r = ($r * 10) + ($n % 10);
+    }
+    return $r;
+}
+
+sub rev2($n)
+{
+    (my $r = reverse("$n")) =~ s/^0+//;
+    return $r;
+}
+
+sub runTest
+{
+    use Test2::V0;
+
+    is( rev1(  2),         2, "Test 1");
+    is( rev1( 20),         2, "Test 2");
+    is( rev1(632),       236, "Test 3");
+    is( rev1(495632), 236594, "Test 6");
+
+    is( rev2(  2),         2, "Test 1");
+    is( rev2( 20),         2, "Test 2");
+    is( rev2(632),       236, "Test 3");
+    is( rev2(495632), 236594, "Test 6");
+
+    done_testing;
+}
+