Submission #4028532

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;

map<int,int> M;
int n;

int Pow(int a, int n){
    int ret = 1, pv = a;
    for(;n;n>>=1){
        if(n & 1) ret = (long long)ret * pv % mod;
        pv = (long long)pv * pv % mod;
    }
    return ret;
}

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin >> n;
    for(int i = 0, x; i < n; i++){
        cin >> x;
        ++M[x];
    }
    for(int i = 1; i <= n; i++){
        --M[abs((i-1) - (n-i))];
    }
    for(auto m : M) if(m.second) return !puts("0");
    cout << Pow(2, n/2) << '\n';
}

Submission Info

Judge Result