LeetCode | Merge k Sorted Lists

タイトル:
Merge 
k
 sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
構想:外ソートのようなアルゴリズムは、直接コードをつけましょう.
タイトル:

/**
 * 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 count = lists.size();
        for(int i = 0; i < lists.size(); i++)
        {
            if(lists[i] == NULL)
            {
                count--;
            }
        }
        
        ListNode * result = NULL;
        ListNode * begin = NULL;
        
        while(count > 0)
        {
            int minPos = -1;
            for(int i = 0; i < lists.size(); i++)
            {
                if(minPos == -1 && lists[i] != NULL)
                {
                    minPos = i;
                }
                else if(minPos != -1 && lists[i] != NULL)
                {
                    minPos = lists[minPos]->val<lists[i]->val?minPos:i;
                }
            }
            if(result == NULL)
            {
                result = lists[minPos];
                begin = result;
            }
            else
            {
                result->next = lists[minPos];
                result = result->next;
            }
            lists[minPos] = lists[minPos]->next;
            if(lists[minPos] == NULL)
            {
                count--;
            }
        };
        return begin;
    }
};