akost · June 20, 2018 09:03 · Jul 2, 2017 · Jul 2, 2017 · Jul 2, 2017
diff --git a/cycle_detection.py b/cycle_detection.py
@@ -1,13 +1,23 @@
 """
 Detect a cycle in a linked list. Note that the head pointer may be 'None' if the list is empty.
 
-A Node is defined as: 
- 
+A Node is defined as:
+
     class Node(object):
         def __init__(self, data = None, next_node = None):
             self.data = data
             self.next = next_node
 """
+import unittest
+
+class Node(object):
+    def __init__(self, data = None, next_node = None):
+        self.data = data
+        self.next = next_node
+
+    def setNext(self, next_node = None):
+        self.next = next_node
+
 
 def has_cycle(head):
     if head == None:
@@ -25,6 +35,34 @@ def has_cycle(head):
 
         tortoise = tortoise.next
         hare = hare.next.next
-        
+
     return False
-
+
+class TestStringMethods(unittest.TestCase):
+
+    def test_loop_empty(self):
+        self.assertEqual(has_cycle(None), False)
+
+    def test_loop(self):
+        self.assertEqual(has_cycle(n5), True)
+
+    def test_no_loop(self):
+        self.assertEqual(has_cycle(m5), False)
+
+
+n1 = Node(1, None)
+n2 = Node(2, n1)
+n3 = Node(3, n2)
+n4 = Node(4, n3)
+n5 = Node(5, n4)
+
+n2.setNext(n4) # Loop
+
+m1 = Node(1, None)
+m2 = Node(2, m1)
+m3 = Node(3, m2)
+m4 = Node(4, m3)
+m5 = Node(5, m4)
+
+
+unittest.main()
diff --git a/cycle_detectipn.py → cycle_detection.py b/cycle_detectipn.py → cycle_detection.py
@@ -20,10 +20,11 @@ def has_cycle(head):
         if hare.next == None:
             return False
 
-        if tortoise == hare.next:
+        if tortoise == hare.next or tortoise == hare.next.next:
             return True
 
         tortoise = tortoise.next
         hare = hare.next.next
 
-    return False
+    return False
+
diff --git a/cycle_detectipn.py b/cycle_detectipn.py
@@ -0,0 +1,29 @@
+"""
+Detect a cycle in a linked list. Note that the head pointer may be 'None' if the list is empty.
+
+A Node is defined as: 
+ 
+    class Node(object):
+        def __init__(self, data = None, next_node = None):
+            self.data = data
+            self.next = next_node
+"""
+
+def has_cycle(head):
+    if head == None:
+        return False
+
+    tortoise = hare = head
+
+    while(tortoise or hare or hare.next):
+
+        if hare.next == None:
+            return False
+
+        if tortoise == hare.next:
+            return True
+
+        tortoise = tortoise.next
+        hare = hare.next.next
+
+    return False