Merge K sorted Lists

class Solution {
public:
    ListNode* mergeKLists(vector<ListNode*>& lists) {
        vector<int>v;

        int n = lists.size();

        for(int i = 0; i<n; i++){
            ListNode * temp = lists[i]; //Head address of ith linkedlist
            while(temp!=NULL){
                v.push_back(temp->val);
                temp = temp->next;
            }

        }
        if(v.size()==0)return NULL;
        sort(v.begin(), v.end());

        ListNode * head = new ListNode();
        head->val = v[0];
        ListNode * itr = head;

        for(int i = 1; i<v.size(); i++ ){
            ListNode * a = new ListNode();
            a->val = v[i];

            itr->next = a;
            itr = a;
        }



        return head;

    }
};