[LeetCode]题解（python）：023-Merge k Sorted Lists

题目来源:

　　https://leetcode.com/problems/merge-k-sorted-lists/

---

题意分析：

　　给定k个有序的链表，将这些链表整合成一个新的有序链表。

---

题目思路：

　　前面我们已经给出了两个有序链表整合的做法。这里，我们不妨用归并排序的想法，把n个链表看成 n/2 和n - n/2的整合，直到n/2 <= 1。时间复杂度是 O(n * （2^log k）) = O(n * k).

---

代码（python）：

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

class Solution(object):
    def mergeTwolists(self,l1,l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        ans = ListNode(0)
        tmp = ans
        if l1 == None and l2 == None:
            return None
        while l1 !=None or l2 != None:
            if l1 == None:
                while l2 != None:
                    tmp.val = l2.val
                    l2 = l2.next
                    if l2 == None:
                        break
                    tmp.next = ListNode(0)
                    tmp = tmp.next
                break
            if l2 == None:
                while l1 != None:
                    tmp.val = l1.val
                    l1 = l1.next
                    if l1 == None:
                        break
                    tmp.next = ListNode(0)
                    tmp = tmp.next
                break
            if l1.val <= l2.val:
                tmp.val = l1.val
                l1 = l1.next
            else:
                tmp.val = l2.val
                l2 = l2.next
            tmp.next = ListNode(0)
            tmp = tmp.next
        return ans
    def mergeKLists(self, lists):
        """
        :type lists: List[ListNode]
        :rtype: ListNode
        """
        size = len(lists)
        if size == 0:
            return None
        if size == 1:
            return lists[0]
        n = size // 2
        tmp1 = self.mergeKLists(lists[:n])
        tmp2 = self.mergeKLists(lists[n:])
        return self.mergeTwolists(tmp1,tmp2)
        

---

转载请注明出处：http://www.cnblogs.com/chruny/p/4872905.html