链表系列之【 链表相交】【环形链表】

面试题 02.07. 链表相交 

//面试题 02.07. 链表相交
func getIntersectionNode(headA, headB *ListNode) *ListNode {
  headA1:=headA
  var alen,blen int
  for headA1!=nil{
    headA1=headA1.Next
    alen++
  }
  headB1:=headB
  for headB1!=nil {
    headB1=headB1.Next
    blen++
  }
  if blen>=alen{
    ba:=blen-alen
    headB2:=headB
    headA2:=headA
    for headB2!=nil{
      if headB2==headA2{
        return headB2
      }
      if ba<=0{
        headA2=headA2.Next
      }
      headB2=headB2.Next
      ba--
    }
  }else{
    al:=alen-blen
    headB2:=headB
    headA2:=headA
    for headA2!=nil{
      if headB2==headA2{
        return headB2
      }
      if al<=0{
        headB2=headB2.Next
      }
      headA2=headA2.Next
      al--
    }
  }
  return nil
}

 142. 环形链表 II

//142. 环形链表 II
func detectCycle(head *ListNode) *ListNode {
  slow, fast := head, head
  for fast!=nil && fast.Next!=nil{
    slow=slow.Next
    fast=fast.Next.Next
    if slow==fast{
      for slow!=head{
        slow=slow.Next
        head=head.Next
      }
      return slow
    }
  }
  return nil
}