148\. 排序链表
# 148. 排序链表 (opens new window)
# Description
Difficulty: 中等
Related Topics: 链表 (opens new window), 双指针 (opens new window), 分治 (opens new window), 排序 (opens new window), 归并排序 (opens new window)
给你链表的头结点 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]
1
2
2
示例 2:
输入:head = [-1,5,3,4,0]
输出:[-1,0,3,4,5]
1
2
2
示例 3:
输入:head = []
输出:[]
1
2
2
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?
# Solution
Language: JavaScript
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var sortList = function(head) {
// 终止条件
if (head == null || head.next == null) {
return head
}
// 获取链表中间节点
let midNode = getMiddleNode(head)
let rightHead = midNode.next
// 断开链表
midNode.next = null
let left = sortList(head)
let right = sortList(rightHead)
// 合并有序链表
return mergeTwoLists(left, right)
};
// 利用快慢指针找到中间节点
var getMiddleNode = function (head) {
if (head == null || head.next == null) {
return head
}
let slow = head
let fast = head.next.next
while (fast != null && fast.next != null) {
slow = slow.next
fast = fast.next.next
}
return slow
}
// 合并两个有序链表
var mergeTwoLists = function (l1, l2) {
let dmy = { next: null }
let curr = dmy
while (l1 != null && l2 != null) {
if (l1.val < l2.val) {
// [curr.next, l1] = [l1, l1.next]
curr.next = l1
l1 = l1.next
} else {
// [curr.next, l2] = [l2, l2.next]
curr.next = l2
l2 = l2.next
}
curr = curr.next
}
curr.next = l1 != null ? l1 : l2
return dmy.next
}
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