From 31dafab6aa001f9fa49e18e4b5cb790c6e104c50 Mon Sep 17 00:00:00 2001
From: gyeo-ri <gyeori.world@gmail.com>
Date: Sat, 2 May 2026 12:48:29 +0900
Subject: [PATCH 1/2] =?UTF-8?q?feat:=20set=EC=9D=84=20=EC=82=AC=EC=9A=A9?=
 =?UTF-8?q?=ED=95=9C=20=ED=92=80=EC=9D=B4?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 linked-list-cycle/gyeo-ri.py | 52 ++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 linked-list-cycle/gyeo-ri.py

diff --git a/linked-list-cycle/gyeo-ri.py b/linked-list-cycle/gyeo-ri.py
new file mode 100644
index 0000000000..15b5052051
--- /dev/null
+++ b/linked-list-cycle/gyeo-ri.py
@@ -0,0 +1,52 @@
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val: int = val
+        self.next: ListNode | None = next
+
+
+class Solution:
+    def hasCycle(self, head: ListNode | None) -> bool:
+        visited_nodes = set()
+        while head is not None:
+            if head in visited_nodes:
+                return True
+
+            visited_nodes.add(head)
+            head = head.next
+        return False
+
+
+if __name__ == "__main__":
+    test_cases = [
+        ([3, 2, 0, -4], 1, True),
+        ([1, 2], 0, True),
+        ([1], -1, False),
+        ([], -1, False),
+    ]
+
+    solution = Solution()
+
+    for idx, (inp, pos, expected) in enumerate(test_cases, start=1):
+        head = None
+        nodes = []
+
+        for value in reversed(inp):
+            head = ListNode(value, head)
+
+        curr = head
+
+        while curr:
+            nodes.append(curr)
+            curr = curr.next
+
+        if pos != -1 and nodes:
+            nodes[-1].next = nodes[pos]
+
+        result = solution.hasCycle(head)
+
+        assert (
+            result == expected
+        ), f"Test Case {idx} Failed: Expected {expected}, Got {result}"
+
+    print("All test cases passed.")

From f4b279589e415afdc2838e7aaeb8c3351c84f16b Mon Sep 17 00:00:00 2001
From: gyeo-ri <gyeori.world@gmail.com>
Date: Sat, 2 May 2026 13:34:15 +0900
Subject: [PATCH 2/2] =?UTF-8?q?feat:=20=ED=8F=AC=EC=9D=B8=ED=84=B0=20?=
 =?UTF-8?q?=EB=B0=A9=EC=8B=9D=EC=9D=98=20=ED=92=80=EC=9D=B4?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 linked-list-cycle/gyeo-ri.py | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/linked-list-cycle/gyeo-ri.py b/linked-list-cycle/gyeo-ri.py
index 15b5052051..3dc2a4fcf1 100644
--- a/linked-list-cycle/gyeo-ri.py
+++ b/linked-list-cycle/gyeo-ri.py
@@ -1,3 +1,14 @@
+"""
+[결과 요약]
+# 시도한 로직 수: 2
+    1. Set을 사용하여 이전 노드를 저장하기(O(n) / O(n))
+        - 메모리를 많이 사용함
+    2. 포인터를 사용하여 메모리 사용량 줄이기(O(n) / O(1)
+        - set 방식과 시간 복잡도(O(n))은 동일하나, 실제 성능은 개선됨
+            - set은 이전 노드 비교를 위해 해시 탐색이 필요하여 상대적으로 성능 저하
+"""
+
+
 # Definition for singly-linked list.
 class ListNode:
     def __init__(self, val=0, next=None):
@@ -7,13 +18,18 @@ def __init__(self, val=0, next=None):
 
 class Solution:
     def hasCycle(self, head: ListNode | None) -> bool:
-        visited_nodes = set()
-        while head is not None:
-            if head in visited_nodes:
+        node_1_step, node_2_steps = head, head
+
+        # 1. 2 steps를 더 이상 탐색할 수 없을 때까지(node is None or node.next is None) 반복
+        while node_2_steps is not None and node_2_steps.next is not None:
+            node_1_step = node_1_step.next
+            node_2_steps = node_2_steps.next.next
+
+            # 2. 계속 돌렸을 때 node 1과 node 2가 만나면 순회가 있는 것
+            # 일치 비교이므로 is 사용
+            if node_1_step is node_2_steps:
                 return True
 
-            visited_nodes.add(head)
-            head = head.next
         return False
 
 
@@ -22,6 +38,7 @@ def hasCycle(self, head: ListNode | None) -> bool:
         ([3, 2, 0, -4], 1, True),
         ([1, 2], 0, True),
         ([1], -1, False),
+        ([1, 2], -1, False),
         ([], -1, False),
     ]