# 147. Insertion Sort List

**<font color=red>难度:Medium<font>**

## 刷题内容
> 原题连接

* https://leetcode.com/problems/insertion-sort-list/

> 内容描述

```
Sort a linked list using insertion sort.


A graphical example of insertion sort. The partial sorted list (black) initially contains only the first element in the list.
With each iteration one element (red) is removed from the input data and inserted in-place into the sorted list
 

Algorithm of Insertion Sort:

Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list.
At each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list, and inserts it there.
It repeats until no input elements remain.

Example 1:

Input: 4->2->1->3
Output: 1->2->3->4
Example 2:

Input: -1->5->3->4->0
Output: -1->0->3->4->5
```

> 思路
******- 时间复杂度: O(N^2)******- 空间复杂度: O(1)******

对链表进行插入排序。和普通的插入排序一样，不过要注意需要对链表的操作很熟悉。当某个值在链表中的位置时需要将这个节点插入到合适的位置，执行依次链表的插入和删除操作。

```cpp
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* insertionSortList(ListNode* head) {
        if(!head)
            return head;
            ListNode* current = head ->next;
        ListNode* pre = head;
        while(current)
        {
            ListNode* temp2 = head;
            ListNode* temp1 = head;
            while(temp2 ->val < current ->val)
            {
                temp1 = temp2;
                temp2 = temp2 ->next;
            }
            if(temp1 != temp2)
                temp1 ->next = current;
            else
                head = current;
            if(temp2 != current)
            {
                pre ->next = current ->next;
                current ->next = temp2;
                current = pre ->next;
            }
            else
            {
                pre = current;
                current = current ->next;
            }
        }
        return head;
    }
};
```