/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
	struct cmp {
		inline bool operator()(ListNode *&x, ListNode *&y) {
			return x->val > y->val;
		}
	};
	ListNode* mergeKLists(vector<ListNode*>& lists) {
		priority_queue<ListNode*, vector<ListNode*>, cmp> q;
		for (auto r : lists) {
			while (r) {
				q.push(r);
				r = r->next;
			}
		}
		ListNode root(0), *p = &root;
		while (!q.empty()) {
			p->next = q.top(); q.pop();
			p = p->next;
		}
		p->next = NULL;
		return root.next;
	}
};