Submission #7092149

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;

const int MAXN = 2e5;
int N;
int cnt[MAXN];

int main() {
	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	
	cin >> N;
	for (int i = 0; i < N; i++) {
		int a; cin >> a;
		cnt[a]++;
	}

	for (int i = 0; i < N; i++) {
		int v = abs(i - (N-1-i));
		if (cnt[v] != 2 - (v == 0)) {
			cout << 0 << '\n';
			exit(0);
		}
	}

	const int MOD = 1e9 + 7;
	int ans = 1;
	for (int i = 0; i < N/2; i++) {
		ans = 2 * ans % MOD;
	}
	cout << ans << '\n';

	return 0;
}

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Judge Result