Given a linked list, determine if it has a cycle in it.
To represent a cycle in the given linked list, we use an integer
pos which represents the position (0-indexed) in the linked list where tail connects to. If
-1, then there is no cycle in the linked list.
Input: head = [3,2,0,-4], pos = 1 Output: true Explanation: There is a cycle in the linked list, where tail connects to the second node.
Input: head = [1,2], pos = 0 Output: true Explanation: There is a cycle in the linked list, where tail connects to the first node.
Input: head = , pos = -1 Output: false Explanation: There is no cycle in the linked list.
If any of the node has been visited, the linked list has a cycle.
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def hasCycle(self, head: ListNode) -> bool: visited = set() while head != None: if head not in visited: visited.add(head) else: return True head = head.next return False
- Time complexity: O(N).
- Space complexity: O(N).