141.E 环形链表

Problem: 141. 环形链表

思路

快慢指针。慢指针指向head，快指针指向head.next，每次分别走1步和2步。

Code

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func hasCycle(head *ListNode) bool {
	if head == nil {
		return false
	}

	slow, fast := head, head.Next
	for fast != slow {
        // 避免空指针
		if fast == nil || fast.Next == nil {
			return false
		}

		slow = slow.Next
		fast = fast.Next.Next
	}

	return true
}