[LeetCode] Merge k Sorted Lists

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

Soluton:

/**

 * 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) {

        int n = lists.size();

        vector<ListNode *> tmp = lists;

        ListNode *ans = NULL, *e = NULL, *t = NULL;

        bool flag = true;

        while(flag)

        {

            int min = 2147483647, index = 0;

            flag = false;

            

            for(int i = 0;i < n;i++)

            {

                if(tmp[i] != NULL)

                {

                    flag = true;

                    if(tmp[i] -> val < min)

                    {

                        min = tmp[i] -> val;

                        index = i;

                    }

                }

            }

            

            if(flag)

            {

                t = tmp[index] -> next;

                tmp[index] -> next = NULL;

                if(ans == NULL) 

                    {

                        ans = tmp[index];

                        e = ans;

                    }

                else

                    {

                        e -> next = tmp[index];

                        e = e -> next;

                    }

                tmp[index] = t;

            }

            else break;

        }

        

        return ans;

    }

};