【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=0;i<lists.size();i++)
        {
            if(lists[i]!=NULL) q.push(lists[i]);
        }
       
        ListNode *front=new ListNode(0);
        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;
       
    }
};