Add solution using hash

data_structures/arrays/jewels_and_stones.rb

@@ -44,6 +44,42 @@ def find_jewels(jewels, stones)
   result
 end
 
+puts find_jewels("aA", "aAAbbbb")
+# => 3
+puts find_jewels("z", "ZZ")
+# => 0
+
+#
+# Approach 2: Hash
+#
+# Time Complexity: O(n)
+#
+
+def find_jewels(jewels, stones)
+  jewels_array = jewels.split('')
+  stones_array = stones.split('')
+  result_hash = {}
+  result = 0
+
+  stones_array.each do |stone|
+    if result_hash[stone] 
+      result_hash[stone] += 1
+    else
+      result_hash[stone] = 1
+    end
+  end
+
+  jewels_array.each do |jewel|
+    if result_hash[jewel]
+      result += result_hash[jewel]
+    else
+      result
+    end
+  end
+
+  result
+end
+
 puts find_jewels("aA", "aAAbbbb")
 # => 3
 puts find_jewels("z", "ZZ")