Merge branch 'master' of github.com:perl6/perl6-examples

Author: L. Grondin

euler/prob149-shlomif.pl

@@ -0,0 +1,153 @@
+use v6;
+
+=begin pod
+
+=head1 DESCRIPTION
+
+Looking at the table below, it is easy to verify that the maximum possible sum
+of adjacent numbers in any direction (horizontal, vertical, diagonal or
+anti-diagonal) is 16 (= 8 + 7 + 1).  −253        2 9−651 3273 −18−4  8
+
+Now, let us repeat the search, b                                        ut on a
+much larger scale:
+
+First, generate four million pseudo-random numbers using a specific form of
+what is known as a "Lagged Fibonacci Generator":
+
+For 1 ≤ k ≤ 55, sk = [100003 − 200003k + 300007k3] (modulo 1000000) − 500000.
+For 56 ≤ k ≤ 4000000, sk = [sk−24 + sk−55 + 1000000] (modulo 1000000) − 500000.
+
+Thus, s10 = −393027 and s100 = 86613.
+
+The terms of s are then arranged in a 2000×2000 table, using the first 2000
+numbers to fill the first row (sequentially), the next 2000 numbers to fill the
+second row, and so on.
+
+Finally, find the greatest sum of (any number of) adjacent entries in any
+direction (horizontal, vertical, diagonal or anti-diagonal).
+
+=end pod
+
+# use integer;
+
+# use Math::BigInt "lib" => "GMP";
+
+class FiboRand {
+    has $.k is rw = 1;
+    has @.last_nums is rw;
+
+    method fetch() {
+        my $k = $.k;
+        my $s_k;
+
+        if ($k <= 55)
+        {
+            $s_k = (((100003 - 200003*$k + 300007*($k**3)) % 1000000) - 500000);
+        }
+        else
+        {
+            $s_k = (((@.last_nums[*-24] + @.last_nums[*-55] + 1000000) % 1000000) - 500000);
+            shift(@.last_nums);
+        }
+        push @.last_nums, $s_k;
+        $.k++;
+
+        return $s_k;
+    }
+}
+
+# Unit test to the randomizer.
+{
+    my $rand = FiboRand.new;
+
+    for 1 .. 9 -> $k
+    {
+        $rand.fetch();
+    }
+
+    if ($rand.fetch() != -393027)
+    {
+        die "Wrong s10!";
+    }
+
+    for 11 .. 99 -> $k
+    {
+        $rand.fetch();
+    }
+
+    if ($rand.fetch() != 86613)
+    {
+        die "Wrong s100!";
+    }
+}
+
+class Max
+{
+    has $.s is rw = 0;
+    has $.e is rw = 0;
+    method add($n)
+    {
+        $.s = max($.s, ($.e = max($.e + $n, 0)));
+
+        return;
+    }
+
+    # g = get()
+    method g()
+    {
+        return $.s;
+    }
+}
+
+my $rand = FiboRand.new;
+
+my $SIZE = 2_000;
+
+my $max_max = 0;
+my @vert_max = map { Max.new }, (1 .. $SIZE);
+my @diag_max = map { Max.new }, (1 .. $SIZE);
+my @anti_diag_max = map { Max.new }, (1 .. $SIZE);
+
+my $diag_offset = 0;
+my $anti_diag_offset = 0;
+
+sub handle_row()
+{
+    my $horiz = Max.new;
+    # First row.
+    for 0 .. $SIZE-1 -> $x
+    {
+        my $s = $rand.fetch();
+
+        @vert_max[$x].add($s);
+        $horiz.add($s);
+        @diag_max[($x+$diag_offset) % $SIZE].add($s);
+        @anti_diag_max[($x+$anti_diag_offset) % $SIZE].add($s);
+    }
+
+    $max_max = max(
+        $max_max, $horiz.g(), @diag_max[0].g(), @anti_diag_max[*-1].g()
+    );
+
+    @diag_max[0] = Max.new;
+    $diag_offset++;
+
+    @anti_diag_max[*-1] = Max.new;
+    $anti_diag_offset--;
+
+    return;
+}
+
+for 1 .. $SIZE -> $y
+{
+    print "Y=$y\n";
+    handle_row();
+}
+
+
+print "Result = ", max(
+    $max_max, (map { $_.g() }, @vert_max, @diag_max, @anti_diag_max
+    )
+), "\n";
+
+# vim: ft=perl6