diff --git a/0141-linked-list-cycle/memo.md b/0141-linked-list-cycle/memo.md
new file mode 100644
index 0000000..a87344e
--- /dev/null
+++ b/0141-linked-list-cycle/memo.md
@@ -0,0 +1,11 @@
+### step1
+
+グラフのサイクル検出アルゴリズムで解こうとしたが、実装が主いつなかったので、ChatGPTに提示されたフロイドの循環検出アルゴリズム（https://note.com/rhayahi/n/n7fc11c09fec6）で解いた。
+
+### step2
+
+L11の部分をhead == nullptrに書き直した。
+
+### step3
+
+step2のコードを3回正解できるまで書き直した。
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diff --git a/0141-linked-list-cycle/solution2.cpp b/0141-linked-list-cycle/solution2.cpp
new file mode 100644
index 0000000..e6d41e8
--- /dev/null
+++ b/0141-linked-list-cycle/solution2.cpp
@@ -0,0 +1,26 @@
+// setを使った別解
+
+// 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) {
+        set<ListNode*> visited;
+        ListNode* curr = head;
+
+        while (curr != nullptr) {
+            if (visited.count(curr)) {
+                return true;
+            }
+            visited.insert(curr);
+            curr = curr->next;
+        }
+
+        return false;
+    }
+};
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diff --git a/0141-linked-list-cycle/step1.cpp b/0141-linked-list-cycle/step1.cpp
new file mode 100644
index 0000000..74d73fc
--- /dev/null
+++ b/0141-linked-list-cycle/step1.cpp
@@ -0,0 +1,26 @@
+// 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) return false;
+
+        ListNode* slow = head;
+        ListNode* fast = head;
+
+        while (fast != nullptr && fast->next != nullptr) {
+            slow = slow->next;
+            fast = fast->next->next;
+
+            if (slow == fast) {
+                return true;
+            }
+        }
+        return false;
+    }
+};
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diff --git a/0141-linked-list-cycle/step2.cpp b/0141-linked-list-cycle/step2.cpp
new file mode 100644
index 0000000..e411c1c
--- /dev/null
+++ b/0141-linked-list-cycle/step2.cpp
@@ -0,0 +1,26 @@
+// 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 == nullptr) return false;
+
+        ListNode* slow = head;
+        ListNode* fast = head;
+
+        while (fast != nullptr && fast->next != nullptr) {
+            slow = slow->next;
+            fast = fast->next->next;
+
+            if (slow == fast) {
+                return true;
+            }
+        }
+        return false;
+    }
+};
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diff --git a/0141-linked-list-cycle/step3.cpp b/0141-linked-list-cycle/step3.cpp
new file mode 100644
index 0000000..888c748
--- /dev/null
+++ b/0141-linked-list-cycle/step3.cpp
@@ -0,0 +1,21 @@
+// 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 == nullptr) return false;
+        ListNode* fast = head;
+        ListNode* slow = head;
+        while (fast != nullptr && fast->next != nullptr) {
+            slow = slow->next;
+            fast = fast->next->next;
+            if (fast == slow) return true;
+        }
+        return false;
+    }
+};
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