Submission #7077817

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Source Code Expand

#include <bits/stdc++.h>
using i64 = long long;

int main() {
    constexpr i64 mod = 1000000007;
    int n;
    std::cin >> n;
    std::vector<int> a(n);
    for (int i = 0; i < n; i++) {
        int in;
        std::cin >> in;
        a[in]++;
    }
    i64 ret = 1;
    for (int i = n - 1; i > 0; i -= 2) {
        if (a[i] != 2) ret = 0;
        else ret = ret * 2 % mod;
    }
    if (a[!(n & 1)] != 2 - n % 2) ret = 0;
    std::cout << ret << std::endl;

    return 0;
}

Submission Info

Judge Result