'''
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

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/insertion-sort-list
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
'''
# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def insertionSortList(self, head: ListNode) -> ListNode:
        if not head:
            return head
        
        Head=ListNode('')
        Head.next=head
        tail=head
        q=tail.next
        tail.next=None #!!!!! this is the best way to avoid fault
        while q:
            if tail.val<=q.val:
                tail.next=q
                q=q.next
                tail=tail.next
                tail.next=None
            else:
                p=Head
                while p.next!=tail and p.next.val<=q.val:p=p.next
                node = q
                q=q.next
                node.next=p.next
                p.next=node
        return Head.next
                