19.1.29 [LeetCode 23] Merge k Sorted Lists

 1 struct cmp {
 2     bool operator () (ListNode *a, ListNode *b) {
 3         return a->val > b->val;
 4     }
 5 };
 6 
 7 class Solution {
 8 public:
 9     ListNode* mergeKLists(vector<ListNode*>& lists) {
10         ListNode*ans=new ListNode(0);
11         ListNode*head = ans;
12         priority_queue<ListNode*, vector<ListNode*>, cmp>q;
13         for (int i = 0; i < lists.size(); i++)
14             if(lists[i])
15                 q.push(lists[i]);
16         while (!q.empty()) {
17             ListNode* tmp = q.top();
18             ans->next = tmp;
19             q.pop();
20             if(tmp->next)
21                 q.push(tmp->next);
22             ans = ans->next;
23         }
24         return head->next;
25     }
26 };