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comparison src/collatz.pl @ 0:307a81e46071 tip

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author Robert McIntyre <rlm@mit.edu>
date Tue, 18 Oct 2011 01:17:49 -0700
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-1:000000000000 0:307a81e46071
1 #!/usr/bin/perl
2
3 use bigint;
4 $a = "/home/r/coderloop-test/euler14-a.in";
5 $b = "/home/r/coderloop-test/euler14-b.in";
6
7 sub read_integer{
8 ##reads an integer from a file
9 (my $file) = @_;
10 my $int;
11 open FILE, "<".$file or die $!;
12 for (<FILE>){ chomp; /^\W*(\d+)\W*$/; $int = $1;}
13 close FILE;
14 return $int;}
15
16
17 @collatz = (1);
18
19
20 sub collatz_next {
21 my $n = @_[0];
22 if (1 == $n) {return 1;}
23 if (0 == ($n % 2)){ return $n/2;}
24 if (1 == ($n % 2)){ return (($n*3)+1);}
25 }
26
27 sub different_collatz_length {
28 my $n = $_[0];
29 my $d = 1;
30 while ($n != 1){
31 $d++;
32 $n = collatz_next($n);}
33 return $d;}
34
35 sub collatz_length {
36 ## calculate the length of the collatz sequence
37 ## http://en.wikipedia.org/wiki/Collatz_conjecture
38 ## starting at n
39 my $n = @_[0];
40 #print $n,"\n";
41 #memoization
42 #print "***** ", $collatz[$n], " ********\n";
43 if (defined $collatz[$n]){return $collatz[$n];}
44 if (1 == $n) {return 1;}
45 if (0 == ($n % 2)){ return (1 + &collatz_length($n/2))}
46 if (1 == ($n % 2)){ return (1 + &collatz_length(($n*3)+1));}
47 }
48
49
50 sub max_collatz {
51 my $n = @_[0];
52 my $max_length = 1;
53 my $max_val = 1;
54 for (my $i = 1; $i < $n; $i++){
55 my $collatz = &different_collatz_length($i);
56 #push(@collatz, $collatz);
57 if ( $collatz >= $max_length){
58 $max_length = $collatz ;
59 $max_val = $i}}
60 print "\n number is : $max_length --- ";
61 print &collatz_length($max_val) . "\n";
62 return $max_val;
63 }
64
65
66
67
68 if (defined @ARGV){
69 print &max_collatz(read_integer($ARGV[0])), "\n";}