Submission #7088378

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Source Code Expand

#include <bits/stdc++.h>
#define ll long long
#define rep(X,N) for(ll X = 0; X < (N); X++)
#define PI (acos(-1.0))
#define pback push_back
#define mpair make_pair
#define MODN 1000000007
#define ALL(V) (V).begin(),(V).end()

using namespace std;


int main(){

    //99点解法は総当たり
    
    int n;
    cin >> n;

    vector<int> c;

    rep(i,n){
        int tmp;
        cin >> tmp;
        c.pback(tmp);
    }

    sort(ALL(c));

    int count = 0;
    int allcount = 0;

    do{
        vector<int> tmpv(8,0);
        rep(i,n - 1){
            int tmp = c[i];

            for(int j = i + 1; j <= n - 1; j++){
                if(c[j] % tmp == 0){
                    tmpv[j]++;
                }
            }
        }

        rep(i,n){
            if(tmpv[i] % 2 == 0) count++;
        }

        allcount++;

    }while(next_permutation(ALL(c)));

    //cerr << count << " " << allcount << endl;

    cout << setprecision(10) << (double)count / allcount << endl;

    return 0;
}

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