题解 | #链表中环的入口结点#

package main
/*
 * type ListNode struct{
 *   Val int
 *   Next *ListNode
 * }
 */

func EntryNodeOfLoop(pHead *ListNode) *ListNode{
    meetNode := GetMeetNode(pHead)
    if meetNode == nil {
        return nil 
    }

    first := pHead
    for i:=0 ;;i++ {
        if first == meetNode {
            return first
        }
        first = first.Next
        meetNode = meetNode.Next
    }
}


func GetMeetNode(head *ListNode) *ListNode {

    fast := head
    slow := head

    for i := 0;;i++ {
        if fast == nil || fast.Next == nil {
            return nil 
        }
        fast = fast.Next.Next
        slow = slow.Next
        if slow == fast {
            return slow
        }
    }
    return nil
}