rlm@0: #!/usr/bin/perl
rlm@0: 
rlm@0: use bigint;
rlm@0: $a = "/home/r/coderloop-test/euler14-a.in";
rlm@0: $b = "/home/r/coderloop-test/euler14-b.in";
rlm@0: 
rlm@0: sub read_integer{
rlm@0:   ##reads an integer from a file
rlm@0:   (my $file) = @_;
rlm@0:   my $int;
rlm@0:   open FILE, "<".$file or die $!;
rlm@0:   for (<FILE>){ chomp; /^\W*(\d+)\W*$/; $int = $1;}
rlm@0:   close FILE;
rlm@0:   return $int;}
rlm@0: 
rlm@0: 
rlm@0: @collatz = (1);
rlm@0: 
rlm@0: 
rlm@0: sub collatz_next {
rlm@0:   my $n = @_[0];
rlm@0:   if (1 == $n) {return 1;}
rlm@0:   if (0 == ($n % 2)){ return $n/2;}
rlm@0:   if (1 == ($n % 2)){ return (($n*3)+1);}
rlm@0: }
rlm@0: 
rlm@0: sub different_collatz_length {
rlm@0:   my $n = $_[0];
rlm@0:   my $d = 1;
rlm@0:   while ($n != 1){
rlm@0:     $d++;
rlm@0:     $n = collatz_next($n);}
rlm@0:   return $d;}
rlm@0: 
rlm@0: sub collatz_length {
rlm@0:   ## calculate the length of the collatz sequence 
rlm@0:   ## http://en.wikipedia.org/wiki/Collatz_conjecture
rlm@0:   ## starting at n
rlm@0:   my $n = @_[0];
rlm@0:   #print $n,"\n";
rlm@0:   #memoization
rlm@0:   #print "***** ", $collatz[$n], " ********\n";
rlm@0:   if (defined $collatz[$n]){return $collatz[$n];}
rlm@0:   if (1 == $n) {return 1;}
rlm@0:   if (0 == ($n % 2)){ return (1 + &collatz_length($n/2))}
rlm@0:   if (1 == ($n % 2)){ return (1 + &collatz_length(($n*3)+1));}
rlm@0: }
rlm@0: 
rlm@0: 
rlm@0: sub max_collatz {
rlm@0:     my $n = @_[0];
rlm@0:     my $max_length = 1;
rlm@0:     my $max_val = 1;
rlm@0:     for (my $i = 1; $i < $n; $i++){
rlm@0: 	my $collatz = &different_collatz_length($i);
rlm@0: 	#push(@collatz, $collatz);
rlm@0: 	if ( $collatz >= $max_length){
rlm@0: 	    $max_length = $collatz ;
rlm@0: 	    $max_val = $i}}
rlm@0:     print "\n number is : $max_length --- ";
rlm@0:     print &collatz_length($max_val) . "\n";
rlm@0:     return $max_val;
rlm@0: }
rlm@0: 
rlm@0: 
rlm@0: 
rlm@0: 
rlm@0: if (defined @ARGV){
rlm@0:     print &max_collatz(read_integer($ARGV[0])), "\n";}