#ifndef S0024_SWAP_NODES_IN_PAIRS
#define S0024_SWAP_NODES_IN_PAIRS

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* swapPairs(ListNode* head);
};

#endif