【leetcode】Merge k Sorted Lists

Merge k Sorted Lists

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

 

采用优先队列priority_queue

把ListNode放入优先队列中，弹出最小指后，如果该ListNode有下一个元素，则把下一个元素放入到队列中

 

 

 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  

10 struct cmp

11 {

12     bool operator()(ListNode *a,ListNode *b)

13     {

14         //升序，每次优先队列返回最小的

15         return a->val>b->val;

16     }

17 };

18  

19 class Solution {

20    

21    

22 public:

23     ListNode *mergeKLists(vector<ListNode *> &lists) {

24        

25         priority_queue<ListNode *,vector<ListNode*>,cmp> q;

26        

27         for(int i=0;i<lists.size();i++)

28         {

29             if(lists[i]!=NULL) q.push(lists[i]);

30         }

31        

32         ListNode *front=new ListNode(0);

33         ListNode *result;

34         result=front;

35        

36         while(!q.empty())

37         {

38             ListNode *tmp=q.top();

39             front->next=tmp;

40             if(tmp->next!=NULL) q.push(tmp->next);

41             q.pop();

42             front=tmp;

43         }

44        

45         front->next=NULL;

46        

47         ListNode *tmp=result;

48         result=result->next;

49         delete tmp;

50         return result;

51        

52     }

53 };