Merge pull request #1515 from aliciabielsa/branch-for-challenge-054

challenge 054 perl

1 files changed, 76 insertions, 0 deletions

diff --git a/challenge-054/alicia-bielsa/perl/ch-2.pl b/challenge-054/alicia-bielsa/perl/ch-2.pl
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+use strict;
+use warnings;
+use Data::Dumper;
+
+# Collatz Conjecture
+# Contributed by Ryan Thompson
+
+# It is thought that the following sequence will always reach 1:
+
+    # $n = $n / 2 when $n is even
+    # $n = 3*$n + 1 when $n is odd
+
+# For example, if we start at 23, we get the following sequence:
+
+# 23 → 70 → 35 → 106 → 53 → 160 → 80 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1
+
+# Write a function that finds the Collatz sequence for any positive integer. 
+#Notice how the sequence itself may go far above the original starting number.
+
+#Have your script calculate the sequence length for all starting numbers up to 1000000 (1e6),
+# and output the starting number and sequence length for the longest 20 sequences.
+
+my %hSequences =();
+for  my $i (1..1000000){
+    my @aSequence =  findCollatzSequence($i);
+    push (@{$hSequences{$i}},@aSequence ) ;
+}
+
+sub findCollatzSequence {
+    my $currentPoint = shift;
+    my $endPoint = 1;
+    my @aSequence = ();
+    while ($currentPoint != $endPoint ){
+        if (exists($hSequences{$currentPoint})){
+            push (@aSequence, @{$hSequences{$currentPoint}});
+            return @aSequence;
+        }
+        push (@aSequence, $currentPoint);
+        if ($currentPoint % 2 == 0){
+            $currentPoint = $currentPoint / 2;
+        } else {
+            $currentPoint = $currentPoint * 3 + 1;
+        }
+    }
+    push (@aSequence, $endPoint);
+    return @aSequence;
+}
+
+ my $count = 20;
+ foreach my $number (sort {scalar(@{$hSequences{$b}}) <=> scalar(@{$hSequences{$a}}) } keys %hSequences) {
+    print "$number\t".scalar(@{$hSequences{$number}})."\n";
+    last if ( $count == 0 );
+    $count--;
+ }
+ 
+# 837799	525
+# 626331	509
+# 939497	507
+# 704623	504
+# 927003	476
+# 910107	476
+# 511935	470
+# 796095	468
+# 767903	468
+# 970599	458
+# 546681	452
+# 820023	450
+# 820022	450
+# 818943	450
+# 410011	449
+# 615017	447
+# 922524	445
+# 906175	445
+# 886953	445
+# 922526	445
+# 938143	445