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Shlomi Fish committed 3845703

Add the solution to Euler #113.

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project-euler/113/euler-113.pl

+#!/usr/bin/perl
+
+use strict;
+use warnings;
+
+=head1 DESCRIPTION
+
+Working from left-to-right if no digit is exceeded by the digit to its left it is called an increasing number; for example, 134468.
+
+Similarly if no digit is exceeded by the digit to its right it is called a decreasing number; for example, 66420.
+
+We shall call a positive integer that is neither increasing nor decreasing a "bouncy" number; for example, 155349.
+
+Clearly there cannot be any bouncy numbers below one-hundred, but just over half of the numbers below one-thousand (525) are bouncy. In fact, the least number for which the proportion of bouncy numbers first reaches 50% is 538.
+
+Surprisingly, bouncy numbers become more and more common and by the time we reach 21780 the proportion of bouncy numbers is equal to 90%.
+
+Find the least number for which the proportion of bouncy numbers is exactly 99%.
+
+=cut
+
+my @counts = (0,0);
+for (my $n = 1; ; $n++)
+{
+    my $s = join "",sort { $a <=> $b } split//,$n;
+
+    $counts[($n eq $s) || ($n eq scalar(reverse($s))) || 0]++;
+
+=begin foo
+    if ($n == 538)
+    {
+        print "@counts\n";
+    }
+=end foo
+
+=cut
+    
+    if ($n % 100_000 == 0)
+    {
+        print "$n: @counts\n"
+    }
+
+    if ($counts[1] * 100 == $n)
+    {
+        print "Least n = $n\n";
+        exit(0);
+    }
+}