Add a zip_with function.

src/advent/util.cr

@@ -1,4 +1,12 @@
 class Array(T)
+  def zip_with(other : Array(R), &block : T, R -> U) forall R, U
+    dest = [] of U
+    zip(other) do |l, r|
+      dest << yield l, r
+    end
+    dest
+  end
+
   def union
     reduce(T.new) do |l, r|
       l | r