[Leetcode][python]Insertion Sort List/对链表进行插入排序

class Solution(object):
    def insertionSortList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return head
        dummy = ListNode(0)
        dummy.next = head
        curr = head
        while curr.next:
            if curr.next.val < curr.val:  # 直到某数小于其前面的数，进入
                pre = dummy  # 回到头开始往后遍历                        
                while pre.next.val < curr.next.val:  # 用pre直到找到应该插入的位置
                    pre = pre.next
                # 如上图
                tmp = curr.next  # 把2保存到temo               
                curr.next = tmp.next # 把4指向2的后面一位
                tmp.next = pre.next  # 2指向3
                pre.next = tmp  # 1指向2
            else:
                curr = curr.next
        return dummy.next