在O(nlogn)的时间复杂度下对一个链表进行排序,通过时间复杂度很容易想到用快排和分治。链表的快排实现比较复杂,这里我们用分治法来实现。代码如下:
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ public class Solution { public ListNode sortList(ListNode head) { if(head == null || head.next == null) return head; ListNode fast = head; ListNode slow = head; while(fast.next != null && fast.next.next != null) { slow = slow.next; fast = fast.next.next; } ListNode node = slow.next; slow.next = null; ListNode left = sortList(head); ListNode right = sortList(node); return merge(left, right); } public ListNode merge(ListNode left, ListNode right) { if(left == null) return right; if(right == null) return left; if(left.val > right.val) { right.next = merge(left, right.next); return right; } else { left.next = merge(left.next, right); return left; } } }