插空问题

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
#define SPO(n) fixed << setprecision(n)
#define endl '\n'
#define ifor(i, l, r) for (long long(i) = (l); (i) <= (r); ++(i))
#define rfor(i, r, l) for (long long(i) = (r); (i) >= (l); --(i))
typedef long long ll;
const int IINF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3f;
const double EPS = 1.0e-9;
const long long MOD = 1e9 + 7;
const long long MAX = 1e5 + 5;


int main() {
//    std::ios::sync_with_stdio(false);
//    cin.tie(0);
//    cout.tie(0);
    int a1[200010];
    int a2[200010];
    int n;

    while (cin >> n) {
        int acc = 0;
        memset(a1, 0, sizeof(a1));
        memset(a2, 0, sizeof(a2));
        ifor(i, 1, 2 * n) {
            a1[i]=i;
        }
        ifor(i, 1, n) {
            swap(a1[i], a2[2 * i]);
        }
        int jj=1;
        ifor(i,n+1,2*n) {
            swap(a1[i], a2[jj]);
            jj+=2;
        }
        acc++;
        int k = 0; //k=1;//a1->a2
        //k=0; a2->a1
        while (1) {
            ifor(i, 1, n) {
                if (k) {
                    swap(a1[i], a2[2 * i]);
                } else {
                    swap(a2[i], a1[2 * i]);
                }
            }
            int j=1;
            ifor(i, n+1, 2*n) {
                if (k) {
                    swap(a1[i], a2[j]);
                } else {
                    swap(a2[i], a1[j]);
                }
                j+=2;
            }
            if(k) k=0;
            else k=1;
            acc++;
            if(a1[1]==1) break;
            else if(a2[1]==1) break;
        }
        cout << acc << endl;
    }
    return 0;
}