#ifndef S0023_MERGE_K_SORTED_LISTS
#define S0023_MERGE_K_SORTED_LISTS

#include <vector>

using namespace std;

struct ListNode {
  int val;
  ListNode* next;
  ListNode() : val(0), next(nullptr) {}
  ListNode(int x) : val(x), next(nullptr) {}
  ListNode(int x, ListNode* next) : val(x), next(next) {}
};

class Solution {
 public:
  ListNode* mergeKLists(vector<ListNode*>& lists);
};

#endif