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 = None

class 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