Submission #1242661

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Source Code Expand

#include <iostream>
#include <sstream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <memory>
#include <complex>
#include <numeric>
#include <cstdio>
#include <iomanip>

#define REP(i,m,n) for(int i=int(m);i<int(n);i++)
#define EACH(i,c) for (auto &(i): c)
#define all(c) begin(c),end(c)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort(begin(c),end(c))
#define pb emplace_back
#define MP make_pair
#define SZ(a) int((a).size())

#ifdef LOCAL
#define DEBUG(s) cout << (s) << endl
#define dump(x)  cerr << #x << " = " << (x) << endl
#define BR cout << endl;
#else
#define DEBUG(s) do{}while(0)
#define dump(x) do{}while(0)
#define BR 
#endif
using namespace std;

using UI = unsigned int;
using UL = unsigned long;
using LL = long long int;
using ULL = unsigned long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VLL = vector<LL>;
using VS = vector<string>;
using PII = pair<int,int>;
using VP = vector<PII>;

//struct edge {int from, to, cost;};

constexpr double EPS = 1e-10;
constexpr double PI  = acos(-1.0);
//constexpr int INF = INT_MAX;

template<class T> inline T sqr(T x) {return x*x;}

long long power(long long x, long long n, long long mod) {
    if (n == 0) return 1;
    if (n % 2 == 0) return power(x * x % mod, n/2, mod);
    else return x * power(x, n-1, mod) % mod;
}

int main() {
    int n;
    cin >> n;
    VI a(n), cnt(n,0);
    REP(i,0,n) cin >> a[i];
    REP(i,0,n) {
        ++cnt[(n-a[i])/2];
        ++cnt[(n+a[i])/2];
    }
    REP(i,0,(n+1)/2) {
        if (!(cnt[i] == 2 || (2 * i + 1 == n && cnt[i] == 1))) {
            cout << 0 << endl;
            return 0;
        }
    }
    cout << power(2,n/2,1000000007) << endl;
    
    return 0;
}

Submission Info

Judge Result