add some exercises

exercises/done/follow_suit.rb

@@ -0,0 +1,35 @@
+#!/usr/bin/env ruby
+
+class Card
+  attr_reader :value, :suit
+
+  def initialize(value, suit)
+    @value = value
+    @suit = suit
+  end
+end
+
+def has_suit?(hand, suit)
+  hand.any? { |card| card.suit == suit }
+end
+
+def valid_follow_card?(hand, lead_card, follow_card)
+  if follow_card.suit == lead_card.suit
+    true
+  elsif has_suit?(hand, lead_card.suit)
+    false
+  else
+    true
+  end
+end
+
+hand = [
+  Card.new("9", "hearts"),
+  Card.new("jack", "clubs"),
+  Card.new("7", "spades")
+]
+
+lead_card = Card.new("king", "hearts")
+
+puts valid_follow_card?(hand, lead_card, hand[0]) # true
+puts valid_follow_card?(hand, lead_card, hand[1]) # false