linked-list-cycle-ii.go

package main

import (
	. "github.com/dimaglushkov/solutions/ADS/list"
)

// source: https://leetcode.com/problems/linked-list-cycle-ii/

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func detectCycle(head *ListNode) *ListNode {
	slow, fast := head, head
	for fast != nil && fast.Next != nil {
		slow, fast = slow.Next, fast.Next.Next
		if slow == fast {
			slow = head
			for slow != fast {
				slow, fast = slow.Next, fast.Next
			}
			return slow
		}
	}

	return nil
}