#include "s0024_swap_nodes_in_pairs.hpp"

ListNode* swapPairs(ListNode* head) {
  if (head == nullptr || head->next == nullptr) {
    return head;
  }
  ListNode *newHead = head->next;
  head->next = swapPairs(newHead->next);
  newHead->next = head;
  return newHead;
}