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剑指OfferII077.链表排序

每天都AC 151

前言:

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题目

给定链表的头结点 head ,请将其按 升序 排列并返回 排序后的链表 。

示例 1:输入:head = [4,2,1,3] 输出:[1,2,3,4]

示例 2:输入:head = [-1,5,3,4,0] 输出:[-1,0,3,4,5]

示例 3:输入:head = [] 输出:[]

提示:链表中节点的数目在范围 [0, 5 * 104] 内

-105 <= Node.val <= 105

进阶:你可以在 O(n log n) 时间复杂度和常数级空间复杂度下,对链表进行排序吗?

注意:本题与主站 148 题相同

解题思路分析

1、快排;时间复杂度O(nlog(n)),空间复杂度O(log(n))

func sortList(head *ListNode) *ListNode {   quickSort(head, nil)   return head}func quickSort(head, end *ListNode) {   if head == end || head.Next == end {      return   }   temp := head.Val   fast, slow := head.Next, head   for fast != end {      if fast.Val < temp {         slow = slow.Next         slow.Val, fast.Val = fast.Val, slow.Val      }      fast = fast.Next   }   slow.Val, head.Val = head.Val, slow.Val   quickSort(head, slow)   quickSort(slow.Next, end)}

2、归并;时间复杂度O(nlog(n)),空间复杂度O(log(n))

func sortList(head *ListNode) *ListNode {   if head == nil || head.Next == nil {      return head   }   slow, fast := head, head.Next   for fast != nil && fast.Next != nil {      slow = slow.Next      fast = fast.Next.Next   }   right := sortList(slow.Next)   slow.Next = nil   left := sortList(head)   return mergeTwoLists(left, right)}func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {   res := &ListNode{}   temp := res   for l1 != nil && l2 != nil {      if l1.Val < l2.Val {         temp.Next = l1         l1 = l1.Next      } else {         temp.Next = l2         l2 = l2.Next      }      temp = temp.Next   }   if l1 != nil {      temp.Next = l1   } else {      temp.Next = l2   }   return res.Next}

3、归并;时间复杂度O(nlog(n)),空间复杂度O(1)

func sortList(head *ListNode) *ListNode {   if head == nil || head.Next == nil {      return head   }   res := &ListNode{Next: head}   cur := head   var left, right *ListNode   length := 0   for cur != nil {      length++      cur = cur.Next   }   for i := 1; i < length; i = i * 2 {      cur = res.Next      tail := res      for cur != nil {         left = cur         right = split(left, i)         cur = split(right, i)         tail.Next = mergeTwoLists(left, right)         for tail.Next != nil {            tail = tail.Next         }      }   }   return res.Next}func split(head *ListNode, length int) *ListNode {   cur := head   var right *ListNode   length--   for length > 0 && cur != nil {      length--      cur = cur.Next   }   if cur == nil {      return nil   }   right = cur.Next   cur.Next = nil   return right}func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {   res := &ListNode{}   temp := res   for l1 != nil && l2 != nil {      if l1.Val < l2.Val {         temp.Next = l1         l1 = l1.Next      } else {         temp.Next = l2         l2 = l2.Next      }      temp = temp.Next   }   if l1 != nil {      temp.Next = l1   } else {      temp.Next = l2   }   return res.Next}
总结

Medium题目,题目同leetcode 148.排序链表

标签: #链表排序的最好时间复杂度