Implements a loop detection method

04_linkedList/ll.py

@@ -173,6 +173,25 @@ class SingleLinkedList():
 			else: # not duplicate
 				element = element.nexti
 
+	def detect_loop(self):
+		"""
+		Returns True if a loop is found in a Linked List
+		"""
+		max_ite = self._size + 1
+		# We basically keep going forward.
+		# If we iterate for more than the size of the list without reaching the end,
+		#  we assume there is a loop somewhere.
+		item = self._root
+		ptr = 0
+		while(ptr < max_ite):
+			if item is None :
+				return False
+			else:
+				item = item.nexti
+				ptr += 1
+		return True
+
+
 	def __len__(self):
 		# Returns the number of elements in the list
 		return self._size

04_linkedList/ll_test.py

@@ -20,7 +20,7 @@ class test_single_linked_list_item(unittest.TestCase):
 
 	def test_has_next(self):
 		a = 12
-        t = SingleListItem(12)
+        t = SingleListItem(a)
 
         self.assertEqual(False, t.has_next())
 
@@ -184,5 +184,23 @@ class test_single_linked_list(unittest.TestCase):
         self.assertEqual(3, len(sl))
         self.assertEqual("2, 1, 3", sl.__str__())
 
+    def test_detect_loop(self):
+
+        sl = SingleLinkedList()
+
+        sl.add(2)
+        sl.add(1)
+        sl.add(3)
+        sl.add(2)
+        sl.add(3)
+        sl.add(1)
+        sl.add(2)
+
+        self.assertEqual(7, len(sl))
+        self.assertEqual(False, sl.detect_loop())
+
+        sl._root.nexti.nexti.nexti.nexti = sl._root
+        self.assertEqual(True, sl.detect_loop())
+
 if __name__ == "__main__":
     unittest.main()