题解 | #NC70 单链表的排序#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 the head node
     * @return ListNode类
     */
    ListNode getTail(ListNode head){
        while(head.next!=null){
            head = head.next;
        }
        return head;
    }
    
    public ListNode sortInList (ListNode head) {
        if(head == null || head.next == null){
            return head;
        }
        // write code here
        ListNode left = new ListNode(-1),mid = new ListNode(-1),right = new ListNode(-1);
        ListNode lt = left,mt = mid,rt = right;
        int v = head.val;
        for(ListNode cur = head; cur != null; cur = cur.next){
            if(cur.val < v){
                lt = lt.next = cur;
            }else if(cur.val == v){
                mt = mt.next = cur;
            }else{
                rt = rt.next = cur;
            }
        }
        rt.next = mt.next = lt.next = null;
        left.next = sortInList(left.next);
        right.next = sortInList(right.next);
        getTail(left).next = mid.next;
        getTail(left).next = right.next;
        return left.next;
    }
}