Merge pull request #5516 from simongreen-net/master

sgreen solutions to challenge 147

6 files changed, 177 insertions, 2 deletions

diff --git a/challenge-147/sgreen/README.md b/challenge-147/sgreen/README.md
index 35c104b123..40c85b3a56 100644
--- a/challenge-147/sgreen/README.md
+++ b/challenge-147/sgreen/README.md
@@ -1,3 +1,3 @@
-# The Weekly Challenge 146
+# The Weekly Challenge 147
 
-Solution by Simon Green. [Blog - 2 Fractions and a Prime](https://dev.to/simongreennet/2-fractions-and-a-prime-4fik)
+Solution by Simon Green. [Blog - Look mum, no inputs 😛](https://dev.to/simongreennet/look-mum-no-inputs-3lon)
diff --git a/challenge-147/sgreen/blog.txt b/challenge-147/sgreen/blog.txt
new file mode 100644
index 0000000000..c3f2893760
--- /dev/null
+++ b/challenge-147/sgreen/blog.txt
@@ -0,0 +1 @@
+https://dev.to/simongreennet/look-mum-no-inputs-3lon
diff --git a/challenge-147/sgreen/perl/ch-1.pl b/challenge-147/sgreen/perl/ch-1.pl
new file mode 100755
index 0000000000..acf41ea5ed
--- /dev/null
+++ b/challenge-147/sgreen/perl/ch-1.pl
@@ -0,0 +1,54 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature 'say';
+
+sub is_prime {
+    my $number = shift;
+
+    # Return true or false if the number is a prime
+    return if $number < 2;
+
+    foreach my $i ( 2 .. sqrt($number) ) {
+        return if $number % $i == 0;
+    }
+
+    # It's a prime
+    return 1;
+}
+
+sub is_trunc_prime {
+    my $number = shift;
+
+    if ( index( $number, '0' ) != -1 ) {
+        # A left-truncatable prime cannot contain a zero
+        return;
+    }
+
+    # Return true or false if the number and all it's left truncated
+    #  parts is a prime. Start with the smallest figure first
+    foreach my $i ( reverse 1 .. length($number) ) {
+        return if not is_prime( substr( $number, $i - 1 ) );
+    }
+
+    return 1;
+}
+
+sub main {
+    my @solutions = ();
+    my $number    = 1;
+
+    # Keep increasing number by one until we have twenty truncated prime
+    #  numbers
+    while ( @solutions < 20 ) {
+        if ( is_trunc_prime($number) ) {
+            push @solutions, $number;
+        }
+        $number++;
+    }
+
+    say join ', ', @solutions;
+}
+
+main();
diff --git a/challenge-147/sgreen/perl/ch-2.pl b/challenge-147/sgreen/perl/ch-2.pl
new file mode 100755
index 0000000000..44fda65617
--- /dev/null
+++ b/challenge-147/sgreen/perl/ch-2.pl
@@ -0,0 +1,38 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature 'say';
+
+sub pentagon_number {
+    my $n = shift;
+    return $n * ( 3 * $n - 1 ) / 2;
+}
+
+sub is_pentagon_number {
+    my $x = shift;
+    my $n = sqrt( 24 * $x + 1 ) + 1;
+    return ( $n == int($n) and $n % 6 == 0 ) ? ( $n / 6 ) : undef;
+}
+
+sub main {
+    my $n1 = 2;
+    while (1) {
+        my $p1 = pentagon_number($n1);
+        foreach my $n2 ( 1 .. $n1 - 1 ) {
+            my $p2 = pentagon_number($n2);
+
+            my $s1 = is_pentagon_number( $p1 + $p2 );
+            my $s2 = is_pentagon_number( $p1 - $p2 );
+
+            if ( defined $s1 and defined $s2 ) {
+                say "P($n1) + P($n2) = $p1 + $p2 = ", $p1 + $p2, "  = P($s1)";
+                say "P($n1) - P($n2) = $p1 - $p2 = ", $p1 - $p2, "  = P($s2)";
+                return;
+            }
+        }
+        $n1++;
+    }
+}
+
+main();
diff --git a/challenge-147/sgreen/python/ch-1.py b/challenge-147/sgreen/python/ch-1.py
new file mode 100755
index 0000000000..1b77f58482
--- /dev/null
+++ b/challenge-147/sgreen/python/ch-1.py
@@ -0,0 +1,50 @@
+#!/usr/bin/env python
+
+import math
+
+
+def is_prime(number):
+    # Return true or false if the number is a prime
+    if number < 2:
+        return False
+
+    for i in range(2, int(math.sqrt(number)) + 1):
+        if number % i == 0:
+            return False
+
+    # It's a prime
+    return True
+
+
+def is_trunc_prime(number):
+    # Return true or false if the number and all it's left truncated
+    #  parts is a prime. Start with the smallest figure first
+    n = str(number)
+
+    if '0' in n:
+        # A left-truncatable prime cannot contain a zero
+        return False
+
+    for i in range(len(n), 0, -1):
+        if not is_prime(int(n[i - 1:])):
+            return False
+
+    return True
+
+
+def main():
+    solutions = []
+    number = 1
+
+    # Keep increasing number by one until we have twenty truncated prime
+    #  numbers
+    while len(solutions) < 20:
+        if is_trunc_prime(number):
+            solutions.append(number)
+        number += 1
+
+    print(*solutions, sep=', ')
+
+
+if __name__ == '__main__':
+    main()
diff --git a/challenge-147/sgreen/python/ch-2.py b/challenge-147/sgreen/python/ch-2.py
new file mode 100755
index 0000000000..c6424b9617
--- /dev/null
+++ b/challenge-147/sgreen/python/ch-2.py
@@ -0,0 +1,32 @@
+#!/usr/bin/env python
+
+import math
+
+
+def pentagon_number(n):
+    return int(n * (3 * n - 1) / 2)
+
+
+def is_pentagon_number(x):
+    n = math.sqrt(24 * x + 1) + 1
+    return int(n / 6) if n % 6 == 0 else None
+
+
+def main():
+    n1 = 2
+    while True:
+        p1 = pentagon_number(n1)
+        for n2 in range(1, n1):
+            p2 = pentagon_number(n2)
+
+            s1 = is_pentagon_number(p1 + p2)
+            s2 = is_pentagon_number(p1 - p2)
+
+            if s1 is not None and s2 is not None:
+                print(f'P({n1}) + P({n2}) = {p1} + {p2} = { p1 + p2 } = P({s1})')
+                print(f'P({n1}) - P({n2}) = {p1} - {p2} = { p1 - p2 } = P({s2})')
+                return
+        n1 += 1
+
+
+main()