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; 

    }

};