Submission #1177510

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Source Code Expand

#include <bits/stdc++.h>

using namespace std;

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)

using ll = long long;
using P = std::tuple<int,int>;

const int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1}, dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};

int cnt[100100];

template <typename T>
T expt(T a, T n, T mod = std::numeric_limits<T>::max()){
    T res = 1;
    while(n){
        if(n & 1){res = res * a % mod;}
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    int N;
    std::cin >> N;

    for(int i=0;i<N;++i){
        int a;
        std::cin >> a;

        ++cnt[a];
    }

    if(cnt[0] > 1){
        std::cout << 0 << std::endl;
        return 0;
    }

    int n = cnt[0];
    for(int i=1;i<N;++i){
        if(cnt[i] == 0 || cnt[i] == 2){
            n += cnt[i];
        }else{
            std::cout << 0 << std::endl;
            return 0;
        }
    }

    if(n == N){
        std::cout << expt(2ll, 1ll * N / 2, 1000000000ll + 7) << std::endl;
    }
}

Submission Info

Judge Result