LeetCode--148--排序链表(python)

在 O(n log n) 时间复杂度和常数级空间复杂度下，对链表进行排序。

示例 1:

输入: 4->2->1->3
输出: 1->2->3->4
示例 2:

输入: -1->5->3->4->0
输出: -1->0->3->4->5

插入排序，肯定超时了，时间复杂度最坏是O(n^2)

 class Solution:
     def sortList(self, head: ListNode) -> ListNode:
         if head==None or head.next==None:
             return head
         dummyY=ListNode(0)
         dummyY.next=head
         p = head
         r = p.next
         p.next=None
         p=r
         while p != None:
             pre = dummyY
             r = p.next
             while pre.next!=None and pre.next.val <p.val:
                 pre = pre.next
             p.next = pre.next
             pre.next = p
             p = r
         return dummyY.next

归并

 class Solution:
     def sortList(self, head: ListNode) -> ListNode:
         if not head or not head.next:return head
         slow,fast = head,head.next
         while fast and fast.next:
             fast,slow=fast.next.next,slow.next
         mid,slow.next=slow.next,None
         left,right=self.sortList(head),self.sortList(mid)

         h=res = ListNode(0)
         while left and right:
             if left.val < right.val :h.next,left=left,left.next
             else:h.next,right=right,right.next
             h=h.next
         h.next=left if left else right
         return res.next