Joelle's solution to 27.1 in Perl 5

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+#!/usr/bin/env perl
+use v5.26;
+use strict;
+use warnings;
+use utf8;    # For unicode comments
+
+# Turn on method signatures
+use feature 'signatures';
+no warnings 'experimental::signatures';
+
+# This program finds the intersection of two lines.  While the word
+# "ends" is used, I'm instead assuming that these are true mathematical
+# lines, not line segments, so the intersection point may not be between
+# the two points that define the line.
+#
+# The first thing we need to do is to find the slope of each line.
+#
+# Edge case 1: If either line is not fully defined, we return an error.
+# This happens if both points are the same.
+#
+# Edge case 2: A vertical line can't be defined by the standard y = A × x₁ + C
+# equation.  In this case we handle it differently, see below.  We use ∞
+# (undef) for the slope in this case.
+#
+# To find the slope (of non-vertical lines), it's just rise / run, which is
+# easy to calculate.  For the constant, we need to solve this:
+#  y = Ax + C
+# A given point will define x and y, while the slope defines A, so we just
+# solve for C.  THus:
+#  C = y - Ax;
+#
+# If we have two equations: y₁ = A₁ × x₁ + C₁
+#                           y₂ = A₂ × x₂ + C₂
+#
+# We can find the intersection:
+#   1) If slope is identical, and constants differ, NO INTERSECTION
+#   2) If slope is identical, and constants are the same, this is the
+#      same line.
+#   3) If the slope is infinite of either line, just solve the other
+#      equation to determine y for that value of x.
+#   4) Otherwise, we're looking for the point where x₁=x₂ and y₁=y₂
+#      Thus, we can rewrite the equations as:
+#       y = A₁ × x + C₁
+#       y = A₂ × x + C₂
+#      We can solve this system for x:
+#       A₁ × x + C₁ = A₂ × x + C₂
+#      Rewritten:
+#       A₁ × x - A₂ × x = C₂ - C₁
+#      Rewritten:
+#       (A₁ - A₂) × x = C₂ - C₁
+#       x = (C₂ - C₁) ÷ (A₁ - A₂)
+#      Once we have x, we can solve for y by plugging into either of the
+#      original equations.
+#
+
+package Point {
+    use Moose;
+    use feature 'signatures';
+    no warnings 'experimental::signatures';
+
+    use Regexp::Common;
+
+    has x => (
+        is       => 'rw',
+        isa      => 'Num',
+        required => 1,
+    );
+
+    has y => (
+        is       => 'rw',
+        isa      => 'Num',
+        required => 1,
+    );
+
+    sub from_string ( $self, $point_str ) {
+        $point_str =~ s/^ \( [.*] \) $/$1/sx;    # Remove parens
+
+        my (@parts) = split ',', $point_str;
+        if ( scalar( grep { /^ $RE{num}{real} $/sx } @parts ) != scalar(@parts) ) {
+            die("Invalid point specification");
+        }
+        die("Invalid point specification") unless scalar(@parts) == 2;
+
+        return $self->new( x => $parts[0], y => $parts[1] );
+    }
+
+    sub eqv ( $self, $point ) {
+        return ( ( $self->x == $point->x ) && ( $self->y == $point->y ) );
+    }
+}
+
+package Line {
+    use Moose;
+    use feature 'signatures';
+    no warnings 'experimental::signatures';
+
+    has slope => (
+        is       => 'rw',
+        isa      => 'Maybe[Num]',
+        required => 1,
+    );
+
+    has point => (
+        is       => 'rw',
+        isa      => 'Point',
+        required => 1,
+    );
+
+    sub solve_for_x ( $self, $y ) {
+        # Vertical line exception
+        return $self->x if !defined $self->slope;
+
+        # Horizontal line exception
+        if ( $self->slope == 0 ) {
+            die "Cannot solve for $y" if $self->point->y != $y;
+        }
+
+        return ( $y - $self->y_offset ) / $self->slope;
+    }
+
+    sub solve_for_y ( $self, $x ) {
+        # Horizontal line exception
+        return $self->point->y if $self->slope == 0;
+
+        # Vertical line exception
+        if ( !defined $self->slope ) {
+            die "Cannot solve for $x" if $self->point->x != $x;
+        }
+
+        # Lines between horizontal and vertical
+        return $self->slope * $x + $self->y_offset;
+    }
+
+    sub y_offset($self) {
+        # Vertical line exception
+        return if !defined $self->slope;
+
+        # Non-vertical lines
+        return $self->point->y - $self->slope * $self->point->x;
+    }
+
+    sub intersection ( $self, $line ) {
+        die "Lines are the same" if $self->eqv($line);
+        if ( defined $self->slope and defined $line->slope ) {
+            die "Lines do not intersect" if $self->slope == $line->slope;
+        }
+
+        # If either line is vertical
+        if ( !defined $self->slope ) {
+            return Point->new( x => $self->point->x, y => $line->solve_for_y( $self->point->x ) );
+        } elsif ( !defined $line->slope ) {
+            return Point->new( x => $line->point->x, y => $self->solve_for_y( $line->point->x ) );
+        }
+
+        # We're finding a normal intersection
+        my $x = ( $line->y_offset - $self->y_offset ) / ( $self->slope - $line->slope );
+        my $y = $self->solve_for_y($x);
+
+        return Point->new( x => $x, y => $y );
+    }
+
+    sub eqv ( $self, $line ) {
+        # Are both vertical?
+        if ( ( !defined $self->slope ) and ( !defined $line->slope ) ) {
+            return $self->point->x == $line->point->x;
+        }
+
+        # Only one is vertical
+        return if ( !defined $self->slope ) or ( !defined $line->slope );
+
+        # All other lines
+        return if $self->slope != $line->slope;
+        return ( $self->point->y == $line->solve_for_y( $self->point->x ) );
+    }
+
+    sub from_points ( $self, $point1, $point2 ) {
+        # Handle same point
+        die "Lines must be defined with two different points" if $point1->eqv($point2);
+
+        # Handle vertical line exception
+        return $self->new( point => $point1, slope => undef ) if $point1->x == $point2->x;
+
+        # Handle other lines.
+        my $slope = ( $point1->y - $point2->y ) / ( $point1->x - $point2->x );
+        return $self->new( point => $point1, slope => $slope );
+    }
+}
+
+# point1 and point2 define a line.  You can determine which line by the
+# letter
+sub MAIN ( $point1a, $point2a, $point1b, $point2b ) {
+    my $line1 = Line->from_points( Point->from_string($point1a), Point->from_string($point2a), );
+    my $line2 = Line->from_points( Point->from_string($point1b), Point->from_string($point2b), );
+
+    if ( $line1->eqv($line2) ) {
+        say "The two lines are the same";
+    } elsif ( ( !defined $line1->slope ) and ( !defined $line2->slope ) ) {
+        say "The two lines don't intersect";
+    } elsif ( defined $line1->slope and defined $line2->slope and $line1->slope == $line2->slope ) {
+        say "The two lines don't intersect";
+    } else {
+        my $intersection = $line1->intersection($line2);
+        say "The lines intersect at (" . $intersection->x . "," . $intersection->y . ")";
+    }
+
+    return;
+}
+
+MAIN(@ARGV);
+