leetcode23.cpp

struct Compare
{
  bool operator() (ListNode* a, ListNode* b){
    return a->val > b->val;
  }
};

class Solution{
  public:
  ListNode* mergeKLists( vector<ListNode*>& lists){
    priority_queue< ListNode*, vector<ListNode*>, Compare> pq;
    
    for(int i=0; i < lists.size() ; i++){
      if(lists[i] !=NULL)
        pq.push(lists[i]);
    }
    
    ListNode head(0);
    ListNode* cur = &head;
    while(!pq.empty()){
      cur->next = pq.top();
      cur = cur->next;
      
      pq.pop();
      if(cur->next !=NULL)
        pq.push(cur->next);
    }
    
    return head.next;
  }
};