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1、暴力法

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* mergeKLists(vector<ListNode*>& lists) {
12 //构建新的数组        
13         vector<int> vec;
14         ListNode *head;
15         for(int i = 0; i < lists.size(); i++){
16             head = lists[i];
17             while ( head != nullptr){
18                 vec.push_back(head->val);
19                 head=head->next;
20             }
21 
22         }
23 //元素为空，后续就没有必要了
24         if (vec.size() == 0 ) return nullptr;
25 //排序，重构链表
26         sort(vec.begin(), vec.end());
27         ListNode  *curr,*temp;
28         ListNode *prev=new ListNode(0);
29         temp=prev;
30         // for (int i = vec.size()-1; i >= 0; i--){           //反序构造链表
31         //     curr = new ListNode(vec[i]);
32         //     curr->next = prev;
33         //     prev = curr;
34 
35 
36         // }
37         for(int i=0;i<vec.size();i++)
38         {
39             curr=new ListNode(vec[i]);                        //正序构造链表
40             prev->next=curr;
41             prev=curr;
42         }
43         return temp->next;
44 
45     }
46 };

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2、分治法，归并排序

 

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