题解

单纯的链表插入排序

import java.util.*;

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

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode insertionSortList (ListNode head) {
        // write code here
        if (head == null || head.next == null) {
            return head;
        }

        ListNode now = head.next;
        head.next = null;
        while (now != null) {
            ListNode injectNode = now;
            now = now.next;
            injectNode.next = null;
            head = insert(head, injectNode);
        }

        return head;
    }

    private ListNode insert(ListNode head, ListNode injectNode) {
        if (injectNode.val < head.val) {
            injectNode.next = head;
            return injectNode;
        }

        ListNode preNode = head;
        ListNode node = head.next;
        while (node != null) {
            if (injectNode.val < node.val) {
                injectNode.next = node;
                preNode.next = injectNode;
                return head;
            }
            preNode = node;
            node = node.next;
        }
        preNode.next = injectNode;
        return head;
    }
}