LeetCode 147. Insertion Sort List

原题链接在这里：https://leetcode.com/problems/insertion-sort-list/

题目：

Sort a linked list using insertion sort.

题解：

与Sort List类似. 

当出现cur.val > cur.next.val时就需要insert cur.next到对应位置.

Time Complexity: O(n^2). Space: O(1).

AC Java:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode insertionSortList(ListNode head) {
        if(head == null || head.next == null){
            return head;
        }
        
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        
        while(head.next != null){
            if(head.val > head.next.val){ //当出现前一个点val 比后一个点val大时，就要找到添加位置
                ListNode mark = dummy;
                while(mark.next != null && mark.next.val<head.next.val){ //找mark位置
                    mark = mark.next;
                }
                
                ListNode temp = head.next;
                head.next = head.next.next;
                temp.next = mark.next;
                mark.next = temp;
            }else{
                head = head.next;
            }
        }
        
        return dummy.next;
    }
}