Leetcode 合并K个排序链表 Python实现

题目要求

合并 k 个排序链表，返回合并后的排序链表。请分析和描述算法的复杂度。

示例:

输入:
[
  1->4->5,
  1->3->4,
  2->6
]
输出: 1->1->2->3->4->4->5->6

解题思路

和合并两个排序链表的基本方式一样，通过递归，进行数组内的链表两两合并，是分治法的一种体现

# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
    def mergeKLists(self, lists):
        length = len(lists)
        if length == 0:
            return None
        if length == 1:
            return lists[0]
        if length == 2:
            return self.mergeParts(lists[0], lists[1])
        
        mid = int(length/2)
        left = self.mergeKLists(lists[0:mid])
        right = self.mergeKLists(lists[mid:length])
        return self.mergeParts(left, right)
        
    def mergeParts(self, l1, l2):
        head = ListNode(0)
        tmp = head
        while l1 and l2:
            if l1.val < l2.val:
                tmp.next = l1
                l1 = l1.next
            else:
                tmp.next = l2
                l2 = l2.next
            tmp = tmp.next
        
        if not l1:
            tmp.next = l2
        if not l2:
            tmp.next = l1
        return head.next