LeetCode_Merge k Sorted Lists

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

　　

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *mergeKLists(vector<ListNode *> &lists) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
       int n = lists.size() ;
        if(n == 0) return NULL;
        if(n == 1) return lists[0];
        
        int *flag = new int[n] ;
        ListNode **list = new ListNode *[n] ;
        int i,min ;
        for(i = 0; i<n;i++)
        {
          if(lists[i] == NULL)
            flag[i] = 0;
          else
            flag[i] = 1;
           
           list[i] = lists[i];
        }
             
        bool stop = true;
        ListNode *head = NULL, *current;
        
        while(stop)
        {
           for(i = 0; i<n &&flag[i] == 0; i++) ;
           
           if(i == n) break;
           min = i ;
           
           for(i++;i<n ;i++)
           {
              if(flag[i]== 0)
                 continue;
              if(list[i]->val < list[min]->val)
                     min = i;
           }
        
           if(head == NULL)
           {
              head = list[min];
              current = list[min];
           }else {
           
              current->next = list[min];
              current = list[min];
           }
           
          list[min] = list[min]->next;
          if(list[min] == NULL) flag[min] = 0;
        }// end of while 
        
        return head; 
    }
};