141. 环形链表

原题

https://leetcode.cn/problems/linked-list-cycle/description/

思路

集合

复杂度

时间：O(n)
空间：O(n)

Python代码

# 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:
        seen = set()
        while head:
            if head in seen:
                return True 
            seen.add(head)
            head = head.next
        return False
        

Go代码

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func hasCycle(head *ListNode) bool {
	seen := make(map[*ListNode]bool)
	for head != nil {
		if seen[head] {
			return true
		}
		seen[head] = true
		head = head.Next
	}
    return false
}