题解 | #对链表进行插入排序#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

/**
 * NC244 对链表进行插入排序
 * @author d3y1
 */
public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @return ListNode类
     */
    public ListNode insertionSortList (ListNode head) {
        // return solution1(head);
        // return solution2(head);
        return solution3(head);
    }

    /**
     * 插入排序
     * @param head
     * @return
     */
    private ListNode solution1(ListNode head){
        if(head == null){
            return null;
        }
        if(head.next == null){
            return head;
        }

        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;
        ListNode cur = head.next;
        head.next = null;

        ListNode pre,tmp;
        while(cur != null){
            pre = dummyHead;
            while(true){
                if(pre.next != null){
                    if(cur.val <= pre.next.val){
                        tmp = cur.next;
                        cur.next = pre.next;
                        pre.next = cur;
                        cur = tmp;
                        break;
                    }else{
                        pre = pre.next;
                    }
                }else{
                    tmp = cur.next;
                    cur.next = pre.next;
                    pre.next = cur;
                    cur = tmp;
                    break;
                }
            }
        }

        return dummyHead.next;
    }

    /**
     * 插入排序: 简化
     * @param head
     * @return
     */
    private ListNode solution2(ListNode head){
        if(head == null){
            return null;
        }
        if(head.next == null){
            return head;
        }

        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;
        ListNode cur = head.next;
        head.next = null;

        ListNode pre,tmp;
        while(cur != null){
            pre = dummyHead;
            while(pre.next!=null && pre.next.val<cur.val){
                pre = pre.next;
            }
            tmp = cur.next;
            cur.next = pre.next;
            pre.next = cur;
            cur = tmp;
        }

        return dummyHead.next;
    }

    /**
     * 插入排序: 再简化
     * @param head
     * @return
     */
    private ListNode solution3(ListNode head){
        ListNode dummyHead = new ListNode(-1);

        ListNode pre,tmp;
        while(head != null){
            pre = dummyHead;
            while(pre.next!=null && pre.next.val<head.val){
                pre = pre.next;
            }
            tmp = head.next;
            head.next = pre.next;
            pre.next = head;
            head = tmp;
        }

        return dummyHead.next;
    }
}