保证AC

#include <iostream>
using namespace std;
int main() {
    int n;
    cin >> n;
    int nums[21000];
    for (int i = 0; i < n; ++i){
        cin >> nums[i];
    }
    for (int i = 0; i < n; i += 2){
        int temp = nums[i];
        nums[i] = nums[i + 1];
        nums[i + 1] = temp;
    }
    for (int i = 0; i < n; ++i){
        cout << nums[i] << " ";
    }
    cout << endl;
}