排序--排序链表

在 O(n log n) 时间复杂度和常数级空间复杂度下，对链表进行排序。

示例 1:
输入: 4->2->1->3
输出: 1->2->3->4

示例 2:
输入: -1->5->3->4->0
输出: -1->0->3->4->5

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python3解答

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def sortList(self, head: ListNode) -> ListNode:
        if not head or not head.next: return head
        slow, fast = head, head.next
        while fast and fast.next:
            fast, slow = fast.next.next, slow.next
        mid, slow.next = slow.next, None
        left, right = self.sortList(head), self.sortList(mid)

        h = res = ListNode(0)
        while left and right:
            if left.val < right.val:
                h.next, left = left, left.next
            else:
                h.next, right = right, right.next
            h = h.next
        h.next = left if left else right
        return res.next