Linked List Cycle/ Linked List Cycle II

Author: gavinfish

141 Linked List Cycle.py

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+'''
+Given a linked list, determine if it has a cycle in it.
+
+Follow up:
+Can you solve it without using extra space?
+'''
+
+# 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
+        """
+        slow = fast = head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            if slow == fast:
+                return True
+        return False
+
+
+if __name__ == "__main__":
+    None

142 Linked List Cycle II.py

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+'''
+Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
+
+Note: Do not modify the linked list.
+
+Follow up:
+Can you solve it without using extra space?
+'''
+
+# Definition for singly-linked list.
+class ListNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+
+class Solution(object):
+    def detectCycle(self, head):
+        """
+        :type head: ListNode
+        :rtype: ListNode
+        """
+        slow = fast = head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            if slow == fast:
+                node = head
+                while node != slow:
+                    node = node.next
+                    slow = slow.next
+                return node
+        return None
+
+
+if __name__ == "__main__":
+    None