Merge k Sorted Lists

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

学习并练习 priority_queue.

priority_queue的几个重要函数 push pop top.

/**
 * 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)
     {
         return a->val > b->val;
     }
 };
class Solution {
public:
    ListNode *mergeKLists(vector<ListNode *> &lists) {
        priority_queue <ListNode* , vector<ListNode*> ,cmp> qu;
        if(lists.size()==0)return NULL;
        for(int i = 0 ; i < lists.size() ; i++)if(lists[i] != NULL)qu.push(lists[i]);
        
        ListNode * head = new ListNode(0), *temp = head;
        head ->next = NULL;
        while(!qu.empty())
        {
            temp -> next = qu.top();
            qu.pop();
            temp = temp->next;
            ListNode * tmp = temp->next;
            if(tmp != NULL)qu.push(tmp);
        }
        return head->next;
        
    }
};