Annotated Challenge #2

challenge-012/dave-jacoby/c2.pl

@@ -0,0 +1,61 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use utf8;
+use feature qw{ postderef say state };
+no warnings qw{ experimental::postderef };
+
+my @paths;
+push @paths, '/a/b/c/d';
+push @paths, '/a/b/cd';
+push @paths, '/a/b/cc';
+push @paths, '/a/b/c/d/e';
+
+# should allow user input and perhaps pull into a subroutine
+# eh, exercise for a reader
+
+# before: ["/a/b/c/d", "/a/b/cd"]
+
+my @p2 = map { [ split m{/} ] } grep { m{^/} } @paths;
+
+# after: [["","a","b","c","d"],["","a","b","c"]]
+
+# while loops are worrying, but this should never go farther than the
+# shortest path in the list
+while (1) {
+    state $c = 0;
+    my $d = 0;
+
+    for my $p (@p2) {
+
+        # first pass, I had separate cases for "end of path"
+        # and "paths separate", but then I stepped back and 
+        # applied more clever
+
+        # I'm checking the nth (or, rather, cth) position in each
+        # array with the same position of the first array, and also
+        # if that's defined. In the case where you have one or more
+        # paths like /a/b/c/d/e/f/g, the answer will be /a/b/c/d/e/f/g
+
+        if ( !defined $p2[$d][$c] || $p2[0][$c] ne $p2[$d][$c] ) {
+
+            # say join '/', $p2[0][ 0 .. $c - 1];
+            #    Use of uninitialized value $. in range (or flip) at ./c2.pl line 43.
+            # which is weird. I guess you cannot get slices of postdereferenced
+            # arrayrefs. Who knew? So we use map instead.
+
+            # and, since there's a problem with $c, we go to $c - 1
+
+            say join '/', map { $p2[0][$_] } 0 .. $c - 1;
+            exit;
+        }
+        $d++;
+    }
+    $c++;
+}
+
+# /a/b
+
+exit;
+