Time: 68 ms (33.08%), Space: 21.4 MB (5.90%) - LeetHub

141-linked-list-cycle/141-linked-list-cycle.py

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+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution(object):
+    def hasCycle(self, head):
+        """
+        :type head: ListNode
+        :rtype: bool
+        """
+        if head == None or head.next == None: return False
+        myDict = {head: 0}
+        point = head
+        while True:
+            point = point.next
+            if point == None: return False
+            if myDict.get(point) == None:
+                myDict[point] = 0
+            else:
+                return True