One-two primes: Difference between revisions

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@@ Line 371: / Line 371: @@
 use ntheory 'is_prime';
-sub condense ($n,$a,$b) { my $i = index($n,$b); $i>9 ? "($a x $i) " . substr($n,$i) : $n }
+sub condense($n) { $n =~ /^((.)\2+)/; my $i = length $1; $i>9 ? "($2 x $i) " . substr($n,$i) : $n }
-sub combine ($d, $a, $b, $s='') {
+sub combine ($d, $a, $b, $s='') {                        # NB: $a < $b
     if      ($d == 1 && is_prime $s.$a) { return $s.$a
     } elsif ($d == 1 && is_prime $s.$b) { return $s.$b
@@ Line 382: / Line 382: @@
 my($a,$b) = (1,2);
 say "Smallest n digit prime using only $a and $b (or '0' if none exists):";
-printf "%4d: %s\n", $_,          combine($_,$a,$b)        for              1..20;
+printf "%4d: %s\n", $_,          combine($_,$a,$b) for             1..20;
-printf "%4d: %s\n", $_, condense(combine($_,$a,$b),$a,$b) for map {100*$_} 1..20;
+printf "%4d: %s\n", $_, condense combine($_,$a,$b) for map 100*$_, 1..20;
 ($a,$b) = (7,9);
 say "\nSmallest n digit prime using only $a and $b (or '0' if none exists):";
-printf "%4d: %s\n", $_, condense(combine($_,$a,$b),$a,$b) for 1..20, 100, 200;
+printf "%4d: %s\n", $_, condense combine($_,$a,$b) for 1..20, 100, 200;
 # 1st term missing