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+# Linked List Cycle
+* 問題: https://leetcode.com/problems/linked-list-cycle/
+* 言語: C++
+* 参考: https://github.com/5103246/LeetCode_Arai60/pull/1/commits/c3cfb1bcf53a4329db7d6afdee8ecb37451860e6
+
+```cpp
+#include <iostream>
+#include <set>
+
+struct ListNode {
+    int val;
+    ListNode* next;
+    ListNode(int x) : val(x), next(nullptr) {}
+};
+
+class Solution {
+    public:
+        bool hasCycle(ListNode *head) {
+            std::set<ListNode*> reached;
+            ListNode* node = head;
+            while (node) {
+                if (reached.contains(node)) {
+                    return true;
+                }
+                reached.insert(node);
+                node = node->next;
+            }
+            return false;
+        }
+};
+```
+
+
+```cpp
+
+/**
+ * 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) {
+            ListNode* fast = head;
+            ListNode* slow = head;
+            while (fast != nullptr && fast->next != nullptr) {
+                if (fast->next != nullptr) {
+                    fast = fast->next->next;
+                    slow = slow->next;
+                    if (fast == slow) {
+                        return true;
+                    }
+                }
+            }
+            return false;
+        }
+};
+
+```