Left factorials: Difference between revisions
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%2 = [128425485935180314, 9157958657951075573395300940314, 20935051082417771847631371547939998232420940314, 620960027832821612639424806694551108812720525606160920420940314, 141074930726669571000530822087000522211656242116439949000980378746128920420940314, 173639511802987526699717162409282876065556519849603157850853034644815111221599509216528920420940314, 906089587987695346534516804650290637694024830011956365184327674619752094289696314882008531991840922336528920420940314, 16695570072624210767034167688394623360733515163575864136345910335924039962404869510225723072235842668787507993136908442336528920420940314, 942786239765826579160595268206839381354754349601050974345395410407078230249590414458830117442618180732911203520208889371641659121356556442336528920420940314, 145722981061585297004706728001906071948635199234860720988658042536179281328615541936083296163475394237524337422204397431927131629058103519228197429698252556442336528920420940314]
2565, 5733, 9128, 12670, 16322, 20062, 23875, 27749, 31678, 35656, </pre>
=={{header|Perl}}==
By caching the last used factorial and left factorial values, I avoid needless recomputation. By only retaining the most recently used values, instead of all past values, I avoid the need to store twenty thousand enormous numbers.
<lang perl>#!perl
use 5.010;
use strict;
use warnings;
use bigint;
sub leftfact {
my ($n) = @_;
state $cached = 0;
state $factorial = 1;
state $leftfact = 0;
if( $n < $cached ) {
($cached, $factorial, $leftfact) = (0, 1, 0);
}
while( $n > $cached ) {
$leftfact += $factorial;
$factorial *= ++$cached;
}
return $leftfact;
}
printf "!%d = %s\n", $_, leftfact($_) for 0 .. 10, map $_*10, 2..11;
printf "!%d has %d digits.\n", $_, length leftfact($_) for map $_*1000, 1..10;
</lang>
Since I copied the printf format strings from the perl6 implementation, the output from the code above is identical to the output of the perl6 code.
=={{header|Perl 6}}==
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