Challenge 54 Solutions

2 files changed, 108 insertions, 0 deletions

diff --git a/challenge-054/mark-anderson/raku/ch-1.p6 b/challenge-054/mark-anderson/raku/ch-1.p6
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+++ b/challenge-054/mark-anderson/raku/ch-1.p6
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+#!/usr/bin/env raku 
+
+sub MAIN(UInt $length, UInt $which) {
+    say ((1..$length).permutations)[$which-1];
+}
diff --git a/challenge-054/mark-anderson/raku/ch-2.p6 b/challenge-054/mark-anderson/raku/ch-2.p6
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+++ b/challenge-054/mark-anderson/raku/ch-2.p6
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+#!/usr/bin/env raku
+
+# Usage: ch-2.p6
+# Output: The length of the 20 longest Collatz sequences from 1 to 1e6.
+
+# 10971  => 268
+# 13255  => 276
+# 17647  => 279
+# 17673  => 279
+# 23529  => 282
+# 26623  => 308
+# 34239  => 311
+# 35497  => 311
+# 35655  => 324
+# 52527  => 340
+# 77031  => 351
+# 106239 => 354
+# 142587 => 375
+# 156159 => 383
+# 216367 => 386
+# 230631 => 443
+# 410011 => 449
+# 511935 => 470
+# 626331 => 509
+# 837799 => 525
+
+# I implemented my own "memoize" with the seen hash.
+# With memoize this program takes about about 90 seconds to run on my pc.
+# Without memoize it takes about 9 and 1/2 minutes.
+
+multi sub MAIN {
+    my $elems; 
+    my @twenty = (1 => 1) xx 20;
+    state %seen;
+
+    for (1 .. 1e6) -> $start {
+        $elems = 0;
+        my $c = collatz_elems($start);
+        %seen{$start} = $c;
+
+        if (@twenty[0].value <= @twenty[19].value <= $c+1) {
+            @twenty.shift;
+            @twenty.push($start => $c+1);
+            @twenty = @twenty.sort({$^a.value <=> $^b.value});
+        }
+    }
+
+    for @twenty -> $pair {
+        say $pair.fmt("%-6s => %s");
+    }
+
+    sub collatz_elems($n is copy --> UInt) {
+        if (%seen{$n}) {
+            return (%seen{$n} + $elems);
+        }
+ 
+        if ($n == 1) { 
+            return $elems;
+        }
+
+        if $n %% 2 {
+            $n = $n / 2; 
+        }
+
+        else {
+            $n = 3 * $n + 1;
+        }
+
+        $elems++;
+        collatz_elems($n);
+    }
+}
+
+# Usage: ch-2.p6 23 
+# Output: The length of the Collatz sequence followed by the sequence.
+# length = 16
+# 23 -> 70 -> 35 -> 106 -> 53 -> 160 -> 80 -> 40 -> 20 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1
+
+multi sub MAIN(UInt $num where $num > 0) {
+    my @arr = collatz_array($num);
+    say "length = {@arr.elems}";
+    say @arr.join(" -> ");
+
+    sub collatz_array($n is copy --> Array) {
+        my @collatz;
+
+        loop {
+            @collatz.push($n);
+
+            if ($n == 1) { 
+                return @collatz;
+            }
+
+            if $n %% 2 {
+                $n = $n / 2; 
+            }
+
+            else {
+                $n = 3 * $n + 1;
+            }
+        }
+    }
+}