[euler] solution for problem 80

Author: andreoss

categories/euler/prob080-andreoss.pl

@@ -0,0 +1,62 @@
+use v6;
+
+=begin pod
+
+=TITLE Square root digital expansion
+
+=AUTHOR Your name (or nick, if you want)
+
+L<https://projecteuler.net/problem=80> 
+
+It is well known that if the square root of a natural number is not an integer, then it is irrational.
+The decimal expansion of such square roots is infinite without any repeating pattern at all.
+The square root of two is 1.41421356237309504880..., and the digital sum of the first one
+hundred decimal digits is 475.
+
+For the first one hundred natural numbers, find the total of the digital sums of the first
+one hundred decimal digits for all the irrational square roots.
+
+The following algoritms was used for the solution:
+L<http://www.afjarvis.staff.shef.ac.uk/maths/jarvisspec02.pdf>
+
+Expected result:  40886
+ 
+=end pod
+
+use v6;
+
+my constant $limit = 100;
+
+sub sqrt-subtraction($n) {
+    my Int $a = $n * 5 ;
+    my Int $b = 5;
+    while $b < 10 * 10 ** $limit {
+	given $a <=> $b {
+	    when More | Same {
+		# replace a with a − b, and add 10 to b.
+		$a -=  $b;
+		$b += 10;
+	    }
+	    when Less {
+		# add two zeros to a
+		$a *= 100; 
+		# add a zero to b just before the final digit (which will always be ‘5’).
+		$b = ($b - (my $x = $b % 10)) * 10 + $x;
+	    }
+	}
+    }
+    $b;
+}
+
+sub MAIN(Bool :$verbose = False) {
+    say [+] do for 1 ... 100 -> $n {
+	next if $n.sqrt.floor ** 2 == $n; 
+	my $x = [+] $n.&sqrt-subtraction.comb[^$limit];
+	say "$n $x"  if $verbose;
+	$x;
+    }
+    say "Done in {now - INIT now}" if $verbose;
+}
+
+
+

t/categories/euler.t

@@ -406,7 +406,14 @@ subtest {
 
     check-example-solutions($problem, $expected-output, @authors)
 }, "prob067";
+subtest {
+    plan  1;
+    my $problem = "prob080";
+    my @authors = <andreoss>;
+    my $expected-output = 40886;
 
+    check-example-solutions($problem, $expected-output, @authors)
+}, "prob080";
 subtest {
     plan 1;