leetcode python3 合并K个排序链表

代码思路:分治思想,K个链表两两配对,合并排序,重复此过程直到合并所有链表

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        res=ListNode(None)
        node=res
        while l1 and l2:
            if l1.val<l2.val:
                node.next,l1 = l1,l1.next
            else:
                node.next,l2 = l2,l2.next
            node=node.next    
        if l1 is not None:
            node.next=l1
        else: 
            node.next=l2
        return res.next  
    
    def mergeKLists(self, lists: List[ListNode]) -> ListNode:
        k=len(lists)
        step=1
        while step < k:
            for i in range(0, k - step, step * 2):
                lists[i] = self.mergeTwoLists(lists[i], lists[i + step])
            step *= 2
        return lists[0] if k > 0 else lists

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