leetcode之Merge k Sorted Lists

这题如果用merge two sorted lists的方法来做的话会十分麻烦的。这里采用的是另外一种就是将所有的sorted list里的数提取出来，排序，然后重新生成一个linked list返回。提取k个sorted list用时O(n),后面的排序用时应该很短，肯定不超O(ologn)。因为k个list都是排好序的，速度会很快。代码如下：

# Definition for singly-linked list.# class ListNode(object):#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution(object):    def mergeKLists(self, lists):        """        :type lists: List[ListNode]        :rtype: ListNode        """        if lists == []:            return None        if len(lists) == 1:            return lists[0]        list1 = []        for i in lists:            while i:                list1.append(i.val)                i = i.next        if list1 == []:            return None        else:            a = ListNode(None)            b = a            list1.sort()            for i in range(len(list1)):                if i != len(list1) - 1:                    b.val = list1[i]                    b.next = ListNode(None)                    b = b.next                else:                    b.val = list1[i]            return a