Leetcode merge-k-sorted-lists（合并k路有序链表 最小堆）

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    static bool cmp(const ListNode *l1, const ListNode *l2)
    {
        return l1->val<l2->val;
    }
    ListNode *mergeKLists(vector<ListNode *> &lists) {
        int n = lists.size();
        ListNode *res = new ListNode(-1);
        if (n<1)
            return res->next;
        if (n<2)
            return lists[0];
        ListNode *p = res;
        int m = 0;
        for(int i=0;i<n;++i)
        {
            if(lists[i]==NULL)
            {
                swap(lists[m],lists[i]);
                m++;
            }
        }
        while(m < n-1)
        {
            sort(lists.begin()+m,lists.end(),cmp);
            p->next=lists[m];
            p=p->next;
            lists[m]=lists[m]->next;
            if(lists[m]==NULL)
            {
                m++;
            }
        }
        if(lists[m]!=NULL)
            p->next=lists[m];
        return res->next;
    }
};