剑指 Offer II 077. 链表排序

剑指 Offer II 077. 链表排序

给定链表的头结点 head ，请将其按 升序 排列并返回 排序后的链表 。

 

解题代码：

class ListNode(object):
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next
        
        
class Solution(object):
    def sortList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if head is None or head.next is None:
            return head
        slow = head
        quick = head.next
        while quick is not None and quick.next is not None:
            quick = quick.next.next
            slow = slow.next
        new_list = slow.next
        slow.next = None
        left_list = self.sortList(head)
        right_list = self.sortList(new_list)
        return self.merge(left_list, right_list)

    def merge(self, left_list, right_list):
        if left_list is None: return right_list
        if right_list is None: return left_list
        if left_list.val < right_list.val:
            left_list.next = self.merge(left_list.next, right_list)
            return left_list
        else:
            right_list.next = self.merge(left_list, right_list.next)
            return right_list