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Author: assassint2017

Linked List Cycle/Linked_List_Cycle.cpp

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+// 双指针 一个快指针，一个慢指针
+// Runtime: 12 ms, faster than 26.05% of C++ online submissions for Linked List Cycle.
+// Memory Usage: 6.7 MB, less than 0.69% of C++ online submissions for Linked List Cycle.
+
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution 
+{
+public:
+    bool hasCycle(ListNode *head) 
+    {
+        if (head == 0)
+            return false;
+
+        ListNode *fastPtr = head->next, *slowPtr = head;
+        
+        while (slowPtr != fastPtr)
+        {
+            if (slowPtr->next != 0 && fastPtr->next != 0 && fastPtr->next->next !=0)
+            {
+                // 慢指针每次一共一格，快指针每次移动两格
+                slowPtr = slowPtr->next;
+                fastPtr = fastPtr->next->next;
+            }
+            else
+                return false;    
+        }
+        return true;
+    }
+};

Linked List Cycle/Linked_List_Cycle.py

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+# Runtime: 68 ms, faster than 18.16% of Python online submissions for Linked List Cycle.
+# Memory Usage: 16.2 MB, less than 89.08% of Python online submissions for Linked List Cycle.
+
+# 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 is None:
+            return False
+        fastPtr = head.next
+        slowPtr = head
+
+        while fastPtr != slowPtr:
+            if slowPtr.next is not None and fastPtr.next is not None and fastPtr.next.next is not None:
+                slowPtr = slowPtr.next
+                fastPtr = fastPtr.next.next
+            else:
+                return False
+        return True