Add initial day6 solution.

day6.cr

@@ -0,0 +1,21 @@
+require "advent"
+INPUT = input(2020, 6).split("\n\n")
+
+def part1
+  input = INPUT.clone
+  answers = input.map do |i|
+    i.chars.uniq!.count &.ascii_letter?
+  end
+  puts answers.sum
+end
+
+def part2
+  input = INPUT.clone
+  sol = input.map do |i|
+    i.split("\n").reject(&.empty?).map(&.chars.to_set).reduce { |s1, s2| s1 & s2 }
+  end
+  puts(sol.map(&.size).sum)
+end
+
+part1
+part2