148. Sort List

难度: Medium

题目描述

Given the head of a linked list, return the list after sorting it in ascending order.

 

Example 1:

Input: head = [4,2,1,3]
Output: [1,2,3,4]

Example 2:

Input: head = [-1,5,3,4,0]
Output: [-1,0,3,4,5]

Example 3:

Input: head = []
Output: []

 

Constraints:

• The number of nodes in the list is in the range [0, 5 * 104].
• -105 <= Node.val <= 105

 

Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?

解题思路

代码实现

解决方案

java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode sortList(ListNode head) {
        List<Integer> list = new ArrayList<>();
        ListNode node = head;
        while (node != null) {
            list.add(node.val);
            node = node.next;
        }
        list.sort(null);
        ListNode res = new ListNode();
        ListNode resP = res;
        for (Integer d : list) {
            ListNode n = new ListNode(d);
            resP.next = n;
            resP = resP.next;
        }
        return res.next;

    }
}