golang力扣leetcode 143.重排链表

package main
type ListNode struct {
  Val  int
  Next *ListNode
}
//找到中点断开，翻转后面部分，然后合并前后两个链表
func reorderList1(head *ListNode) {
  if head == nil {
    return
  }
  mid := findMiddle(head)
  tail := mid.Next
  mid.Next = nil
  tail = reverseList(tail)
  mergeTwoLists(head, tail)
}
//快慢指针找中点
func findMiddle(head *ListNode) *ListNode {
  slow := head
  fast := head.Next
  for fast != nil && fast.Next != nil {
    slow = slow.Next
    fast = fast.Next.Next
  }
  return slow
}
//翻转链表
func reverseList(head *ListNode) *ListNode {
  curr := head
  var p *ListNode
  for curr != nil {
    next := curr.Next
    curr.Next = p
    p = curr
    curr = next
  }
  return p
}
//l1链表插一个，l2链表插1个，依次添加
func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
  dummy := &ListNode{}
  head := dummy
  var f bool = true
  for l1 != nil && l2 != nil {
    if f {
      head.Next = l1
      l1 = l1.Next
    } else {
      head.Next = l2
      l2 = l2.Next
    }
    f = !f
    head = head.Next
  }
  if l1 != nil {
    head.Next = l1
    l1 = l1.Next
    head = head.Next
  } else if l2 != nil {
    head.Next = l2
    l2 = l2.Next
    head = head.Next
  }
  return dummy.Next
}
//重建该链表
func reorderList2(head *ListNode) {
  if head == nil {
    return
  }
  var nodes []*ListNode
  for node := head; node != nil; node = node.Next {
    nodes = append(nodes, node)
  }
  i, j := 0, len(nodes)-1
  for i < j {
    nodes[i].Next = nodes[j]
    i++
    if i == j {
      break
    }
    nodes[j].Next = nodes[i]
    j--
  }
  nodes[i].Next = nil
}
func main() {
  reorderList1(nil)
  reorderList2(nil)
}