Truncatable primes: Difference between revisions

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 =={{header|Perl 6}}==
+<lang perl6>my @primes := 2, 3, 5, -> $p {
-{{works with|Rakudo Star|2010.09}}
+    ($p+2, $p+4 ... -> $i { $i %% none @primes ... * >= sqrt $i })[*-1]
+} ... *;
+sub prime($i) { (state @)[$i] //= $i %% none @primes ... * >= sqrt $i }
-This uses a fairly naive isprime routine. It works but is slow.
+sub ltp {
-<lang perl6>
+    for (9...1) X (9...1) X (9...1) X (9...1) X (9...1) X (9,7,3) -> $a,$b,$c,$d,$e,$f {
-use v6;
-my %cache = <2 3 5 7 11 13 17 19 23> >>=>>> 1;
+	my @x := [\+] $f, $e, $d, $c, $b, $a Z* (1,10,100 ... *);
+        return @x[*-1] if prime @x[0] && prime @x[1] && prime @x[2] &&
+			  prime @x[3] && prime @x[4] && prime @x[5];
-sub isprime ($test) {
+    }
-    return %cache{$test} if defined %cache{$test};
-    return (%cache{$test} = 0) if $test <= 25;
-    my $r = floor($test ** .5);
-    return (%cache{$test} = 0) unless $test % $_ for (2, 3, * + 2 ... * >= $r);
-    return (%cache{$test} = 1);
 }
-sub trunc_prime ($type, $limit is copy) {
+sub infix:<*+> ($a,$b) { $a * 10 + $b }
-    $limit += ($limit % 2 ?? 0 !! 1);
+sub rtp {
-    for ($limit, * - 2 ... * < 2 ) -> $loop {
+    for 7,5,3 {
-        next if $loop ~~ /0/; # No zeros allowed
+	for grep &prime, ($_ X*+ 9,7,3,1) {
-        my $this = $loop;
-        while $this.&isprime {
+	    for grep &prime, ($_ X*+ 9,7,3,1) {
+		for grep &prime, ($_ X*+ 9,7,3,1) {
-            $this.=subst($type, '');
+		    for grep &prime, ($_ X*+ 9,7,3,1) {
-            return $loop unless $this;
+			for grep &prime, ($_ X*+ 9,7,3,1) {
-        }
+			    return $_;
+			}
+		    }
+		}
+	    }
+	}
     }
 }
+say "Highest ltp: ", ltp;
-say "Largest Left  Truncatable Prime < 1000000: ",trunc_prime(rx/^\d/, 1000000);
+say "Highest rtp: ", rtp;</lang>
-say "Largest Right Truncatable Prime < 1000000: ",trunc_prime(rx/\d$/, 1000000);
+{{out}}
-</lang>
+<pre>Highest ltp: 999983
-Output:
+Highest rtp: 739399</pre>
-<pre>
-Largest Left  Truncatable Prime < 1000000: 998443
-Largest Right Truncatable Prime < 1000000: 739339
-</pre>
 =={{header|PicoLisp}}==