<算法>基于三路划分的链表快速排序

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此算法基于三路划分的快速排序的思想，如果不懂请先看我之前的博客：
http://blog.csdn.net/gpwner/article/details/76039533

但是又不完全和之前将的三路划分完全一样

下面开始进入正题：
首先得到一个链表之后，我们将链表拆分为小于、等于、大于头结点的子链表：
这里写图片描述

然后再递归调用算法，将小链表和大链表进行排序，最后再将链表连接成一个与原来的链表一样的链表。

递归结束的条件是：

头结点为null或者链表只有一个节点（也就是说只有头结点）

链表节点的定义：

/** * @version 2017/7/30 14:57 */public class ListNode {    int val;    ListNode next;    ListNode(int x) {        val = x;    }}

public class Main {    public static void main(String[] args) {        Main main = new Main();        ListNode node1 = new ListNode(10);        ListNode node2 = new ListNode(5);        ListNode node3 = new ListNode(2);        ListNode node4 = new ListNode(11);        ListNode node5 = new ListNode(2);        ListNode node6 = new ListNode(8);        ListNode node7 = new ListNode(9);        ListNode node8 = new ListNode(7);        ListNode node9 = new ListNode(6);        node1.next = node2;        node2.next = node3;        node3.next = node4;        node4.next = node5;        node5.next = node6;        node6.next = node7;        node7.next = node8;        node8.next = node9;        node1 = main.sortList(node1);        while (node1 != null) {            System.out.print(node1.val + " ");            node1 = node1.next;        }    }    public ListNode sortList(ListNode head) {        if (head == null || head.next == null)            return head;        int val = head.val;        ListNode smaller = null;        ListNode smaller_head = null;        ListNode mid = head;        ListNode larger = null;        ListNode larger_head = null;        ListNode iter = head.next;        while (iter != null) {            //大于头结点            if (iter.val < val) {                if (smaller_head == null) {                    smaller_head = iter;                } else {                    smaller.next = iter;                }                smaller = iter;                //等于头结点            } else if (iter.val == val) {                mid.next = iter;                mid = iter;                //小于头结点            } else {                if (larger_head == null) {                    larger_head = iter;                } else {                    larger.next = iter;                }                larger = iter;            }            iter = iter.next;        }        //将小链表的末端指针置为null        if (smaller != null)            smaller.next = null;        //将大链表的末指针置为null        if (larger != null)            larger.next = null;        mid.next = sortList(larger_head);        //可能会出现头结点是最小的节点的情况        if (smaller == null) {            return head;        }        smaller_head = sortList(smaller_head);        smaller = smaller_head;        while (smaller.next != null)            smaller = smaller.next;        //将小链表重新连接上        smaller.next = head;        return smaller_head;    }}

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