题目：

题解：

class Solution:
    def sortList(self, head: ListNode) -> ListNode:
        def merge(head1: ListNode, head2: ListNode) -> ListNode:
            dummyHead = ListNode(0)
            temp, temp1, temp2 = dummyHead, head1, head2
            while temp1 and temp2:
                if temp1.val <= temp2.val:
                    temp.next = temp1
                    temp1 = temp1.next
                else:
                    temp.next = temp2
                    temp2 = temp2.next
                temp = temp.next
            if temp1:
                temp.next = temp1
            elif temp2:
                temp.next = temp2
            return dummyHead.next
        
        if not head:
            return head
        
        length = 0
        node = head
        while node:
            length += 1
            node = node.next
        
        dummyHead = ListNode(0, head)
        subLength = 1
        while subLength < length:
            prev, curr = dummyHead, dummyHead.next
            while curr:
                head1 = curr
                for i in range(1, subLength):
                    if curr.next:
                        curr = curr.next
                    else:
                        break
                head2 = curr.next
                curr.next = None
                curr = head2
                for i in range(1, subLength):
                    if curr and curr.next:
                        curr = curr.next
                    else:
                        break
                
                succ = None
                if curr:
                    succ = curr.next
                    curr.next = None
                
                merged = merge(head1, head2)
                prev.next = merged
                while prev.next:
                    prev = prev.next
                curr = succ
            subLength <<= 1
        
        return dummyHead.next