linked-list-cycle sol (py)

Author: hi-rachel

linked-list-cycle/hi-rachel.py

@@ -0,0 +1,40 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+"""
+TC: O(n)
+SC: O(n)
+"""
+class Solution:
+    def hasCycle(self, head: Optional[ListNode]) -> bool:
+        visited = set()
+        while head:
+            # 해당 노드 이미 방문한 적 있으면
+            if head in visited:
+                return True
+            # 방문한 적 없으면 set에 넣기
+            visited.add(head)
+            # 다음 노드로 이동
+            head = head.next
+
+        # cycle이 없음
+        return False
+
+"""
+The tortoise and hare
+
+TC: O(n)
+SC: O(1)
+""" 
+class Solution:
+    def hasCycle(self, head: Optional[ListNode]) -> bool:
+        slow, fast = head, head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            if slow == fast:
+                return True
+        return False