[数据结构与算法]147. 对链表进行插入排序

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def insertionSortList(self, head: ListNode) -> ListNode:
        if not head:
            return head
        
        dummyh = ListNode(0)
        dummyh.next = head
        lastO = head
        curr = lastO.next

        while curr:
            if lastO.val <= curr.val:
                lastO = lastO.next
            else:
                preO = dummyh
                while preO.next.val <= curr.val:
                    preO = preO.next
                lastO.next = curr.next
                curr.next = preO.next
                preO.next = curr
            curr = lastO.next
        
        return dummyh.next

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