package algorithms;

/**

* @Auther: Jesper

* @Date: 2019/2/13 15:42

* @Description: 单链表的快排

*

* 我们只需要两个指针p1和p2，这两个指针均往next方向移动，移动的过程中保持p1之前的key都小于选定的key，p1和p2之间的key都大于选定的key，那么当p2走到末尾时交换p1与key值便完成了一次切分。

*/

public class QuickSortList {

class ListNode {

ListNode next;

int val;

}

public ListNode sortList(ListNode head){

//采用快速排序

quickSort(head, null);

return head;

}

public static void quickSort(ListNode head, ListNode end){

if (head != end){

ListNode node = partion(head, end);

quickSort(head, node);

quickSort(node.next, end);

}

}

public static ListNode partion(ListNode head, ListNode end){

ListNode p1 = head, p2 = head.next;

//走到末尾才停

while (p2 != end){

//大于key值时，p1向前走一步，交换p1与p2的值

if (p2.val < head.val){

p1 = p1.next;

int temp = p1.val;

p1.val = p2.val;

p2.val = temp;

}

p2 = p2.next;

}

//当有序时，不交换p1和key值

if (p1 != head){

int temp = p1.val;

p1.val = head.val;

head.val = temp;

}

return p1;

}

}