LeetCode_142_LinkedListCycle2.md

LeetCode 142: Linked List Cycle II

• Link to Problem

Solution

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

    var hasCycle = false
    for fast.Next != nil && fast.Next.Next != nil {
        slow = slow.Next
        fast = fast.Next.Next
        if slow == fast {
            hasCycle = true
            break
        }
    }
    
    if !hasCycle {
        return nil
    }

    slow = head
    for slow != fast {
        slow = slow.Next
        fast = fast.Next
    }
    return slow
}