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It's not a hard problem to solve:

```#! perl -slw
use strict;
use Time::HiRes qw[ time ];

my \$start = time;

my @res;
for ( 1 .. 1e6 ) {
my \$c = 0;
my \$n = \$_;
while( \$n > 1 ) {
++\$c;
\$n = \$n&1 ? 3*\$n+1 : \$n/2;
if( defined \$res[ \$n ] ) {
\$c += \$res[ \$n ];
last;
}
}
\$res[ \$_ ] = \$c;
}

printf "Took %.6f seconds\n", time() - \$start;

my( \$n, \$i ) = 0;
\$n < \$res[ \$_ ] and ( \$n, \$i ) = ( \$res[ \$_ ], \$_ )
for 1 .. \$#res;

print "longest sequence is \$n steps starting with \$i";

__END__
c:\test>collatz.pl
Took 2.000000 seconds
longest sequence is 524 steps starting with 837799

And the OP gave a link to his own 3 second solution, though I'm not sure why he pastebin'd it rather than posting it here.

The intriguing thing is why the OP felt the need for bigint in the first place given that using Perl's native scalars he could calculate this(*) for numbers up to 2,251,799,813,685,248 before running into precision problems.

(*)Assuming of course he had 400+ years and the exabytes of ram required to store the hash :)

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^2: bigint == horrible performance? by BrowserUk
in thread bigint == horrible performance? by moodywoody

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