【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

 

 

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     ListNode *next;
  *     ListNode(int x) : val(x), next(NULL) {}
  * };
  */

 struct cmp
 {
     bool operator()(ListNode *a,ListNode *b)
     {
         //升序，每次优先队列返回最小的
         return a->val>b->val;
     }
 };

 class Solution {

 public:
     ListNode *mergeKLists(vector<ListNode *> &lists) {

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

         for(int i=;i<lists.size();i++)
         {
             if(lists[i]!=NULL) q.push(lists[i]);
         }

         ListNode *front=new ListNode();
         ListNode *result;
         result=front;

         while(!q.empty())
         {
             ListNode *tmp=q.top();
             front->next=tmp;
             if(tmp->next!=NULL) q.push(tmp->next);
             q.pop();
             front=tmp;
         }

         front->next=NULL;

         ListNode *tmp=result;
         result=result->next;
         delete tmp;
         return result;

     }
 };