so simple

Author: springuper

linkedListCycle.py

@@ -0,0 +1,32 @@
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+# @param head, a ListNode
+# @return a boolean
+def hasCycle(head):
+    fast = head
+    slow = head
+    while fast != None and fast.next != None and slow != None:
+        fast = fast.next.next
+        slow = slow.next
+        if fast == slow:
+            return True
+    return False
+
+a = ListNode('a')
+b = ListNode('b')
+c = ListNode('c')
+d = ListNode('d')
+a.next = b
+b.next = c
+c.next = d
+d.next = b
+assert hasCycle(a) == True
+
+e = ListNode('e')
+f = ListNode('f')
+e.next = f
+assert hasCycle(e) == False