Sockets - Jansen

lib/array_intersection.rb

@@ -1,6 +1,59 @@
 # Returns a new array to that contains elements in the intersection of the two input arrays
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(m^2) + O(n log m), where n is the length of the shorter array, and m is the length of the longer array
+# Space complexity: Linear or O(n) if n < m  (where n is the length of the shorter array, and m is the length of the longer array)
 def intersection(array1, array2)
-  raise NotImplementedError
+  return [] if array1 == nil || array2 == nil
+
+  # Figure out which array is longer (so longest will be sorted)
+  # (If they're the same, array1 will be sorted)
+  if array1.length > array2.length || array1.length == array2.length
+    longer_sorted_array = array1
+    shorter_array = array2
+  else
+    longer_sorted_array = array2
+    shorter_array = array1
+  end
+
+  # Sort larger array
+  i = 1
+  while i < longer_sorted_array.length
+    to_insert = longer_sorted_array[i]
+    j = i
+
+    # searching for correct position to insert longer_sorted_array[j]
+    while j > 0 && longer_sorted_array[j - 1] > to_insert
+      longer_sorted_array[j] = longer_sorted_array[j - 1]
+      j -= 1
+    end
+
+    longer_sorted_array[j] = to_insert
+    i += 1
+  end
+
+  # For each element in smaller array, perform binary search in sorted array
+  results = []
+
+  shorter_array.each do |num|
+    low = 0
+    high = longer_sorted_array.length - 1
+
+    while low < high
+      mid = (low + high) / 2
+      if longer_sorted_array[mid] == num
+        results << num
+        break
+      elsif longer_sorted_array[mid] > num
+        high = mid - 1
+      elsif longer_sorted_array[mid] < num
+        low = mid + 1
+      end
+
+      if longer_sorted_array[low] == num
+        results << num
+        break
+      end
+    end
+  end
+
+  return results
 end