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#include <bits/stdc++.h>
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 *swapPairs(ListNode *head) {
    if (!head || !head->next)
      return head;
    ListNode *temp = new ListNode;
    ListNode *prev = temp;
    ListNode *curr = head;
    while (curr && curr->next) {
      prev->next = curr->next;
      curr->next = prev->next->next;
      prev->next->next = curr;
      prev = curr;
      curr = curr->next;
    }
    return temp->next;
  }
};

int main() {}