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Sort a linked list in O(n log n) time using constant space complexity.
算法思想：
时间复杂度为O(nlogn)的排序算法，有快排、归并、堆排序，快排需要往前遍历，因此不适合单链表，堆排序可以，但是需要O(n)的空间，因此本题的最佳答案应该是归并排序。
与Array的merge sort思想完全一致。
代码如下：
1 public class Solution { 2 public ListNode sortList(ListNode head) { 3 if(head == null || head.next == null) return head; 4 ListNode hhead = new ListNode(0); 5 hhead.next = head; 6 ListNode fast = hhead; 7 ListNode slow = hhead; 8 while(fast != null && fast.next != null){ 9 fast = fast.next.next; 10 slow = slow.next; 11 } 12 ListNode right = slow.next; 13 slow.next = null; 14 ListNode left = sortList(head); 15 right = sortList(right); 16 return merge(left, right); 17 } 18 private ListNode merge(ListNode l1,ListNode l2){ 19 ListNode hhead = new ListNode(0); 20 hhead.next = l1; 21 ListNode p = hhead; 22 while(p.next != null){ 23 if(p.next.val > l2.val){ 24 ListNode tem = l2; 25 l2 = l2.next; 26 tem.next = p.next; 27 p.next = tem; 28 }else 29 p = p.next; 30 if(l2 == null) return hhead.next; 31 } 32 p.next = l2; 33 return hhead.next; 34 } 35 }
[leetcode]Sort List,布布扣,bubuko.com
标签：style blog http color io re
原文地址：http://www.cnblogs.com/huntfor/p/3859375.html
