feat: solve #225 with python

linked-list-cycle/EGON.py

@@ -0,0 +1,47 @@
+from typing import Optional
+from unittest import TestCase, main
+
+
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+
+class Solution:
+    def hasCycle(self, head: Optional[ListNode]) -> bool:
+        return self.solve(head)
+
+    """
+    Runtime: 37 ms (Beats 93.02%)
+    Time Complexity: O(n)
+        > head부터 next가 있는 동안 선형적으로 조회하므로 O(n)
+
+    Memory: 18.62 (Beats 98.22%)
+    Space Complexity: O(1)
+        > head를 제외하고 아무 변수도 사용하지 않았으므로 O(1)
+    """
+    def solve(self, head: Optional[ListNode]) -> bool:
+        if not head:
+            return False
+
+        while head.next:
+            if head.next and head.next.val is None:
+                return True
+
+            head.val = None
+            head = head.next
+
+        return False
+
+
+class _LeetCodeTestCases(TestCase):
+    def test_1(self):
+        head = None
+        output = False
+        self.assertEqual(Solution().hasCycle(head), output)
+
+
+if __name__ == '__main__':
+    main()