Sockets - Sarah

lib/array_intersection.rb

@@ -1,6 +1,63 @@
 # Returns a new array to that contains elements in the intersection of the two input arrays
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n) where n is the length of the longer array
+# Space complexity: O(n) where n is the length of shorter array.
+# its 2n, because of the space of the hash is linear to the shorter array, and the
+# intersection array space is also linear to the smaller array
+
 def intersection(array1, array2)
-  raise NotImplementedError
+  return [] if array1 == nil || array2 == nil
+  if array1.length < array2.length
+    shorter = array1
+    longer = array2
+  else
+    shorter = array2
+    longer = array1
+  end
+  num_hash = Hash.new
+  intersection_array = []
+  shorter.length.times do |index|
+    num_hash[shorter[index]] = 1
+  end
+  longer.length.times do |index|
+    intersection_array << longer[index] if num_hash[longer[index]]
+  end
+
+  return intersection_array
 end
+
+# SORTING SOLUTION
+
+# Returns a new array to that contains elements in the intersection of the two input arrays
+# Time complexity: O(n log n) where n is the size of the smaller array,
+# this is because the highest time complexity is the sruby sort method, which it n log n
+# Space complexity: O(n) where n is the length of the smaller array
+
+# def intersection(array1, array2)
+#   return [] if array1 == nil || array2 == nil
+#   if array1.length < array2.length
+#     array1.sort!
+#     shorter = array1
+#     longer = array2
+#   else
+#     array2.sort!
+#     shorter = array2
+#     longer = array1
+#   end
+#   new_array = []
+#   longer.length.times do |index|
+#     new_array << longer[index] if binary_search(shorter, shorter.length, longer[index])
+#   end
+#   return new_array
+# end
+
+# def binary_search(array, length, value_to_find)
+#   high = length
+#   low = 0
+#   length.times do
+#     guess = (low + high) / 2
+#     return true if array[guess] == value_to_find
+#     return false if high - low <= 1
+#     array[guess] < value_to_find ? low = guess : high = guess
+#   end
+#   return false
+# end