Day 01

Author: petertseng

01_equal_to_next.rb

@@ -0,0 +1,10 @@
+def match(input, dist:)
+  # Doesn't matter whether we go forward or backward,
+  # (either way we get a yes on one half of the matching pair)
+  # so let's go backward to take advantage of negative index.
+  input.each_char.select.with_index { |c, i| c == input[i - dist] }.sum(&method(:Integer))
+end
+
+input = (!ARGV.empty? && ARGV.first.match?(/^\d+$/) ? ARGV.first : ARGF.read).chomp.freeze
+
+[1, input.size / 2].each { |n| puts match(input, dist: n) }