Submission #1532938

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Source Code Expand

#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,x,n) for(int i=x;i<n;i++)
#define ALL(v) (v).begin(),(v).end()
typedef long long LL;
typedef pair<int, int> PI;
typedef vector<int> VI;
const LL MOD = 1000000007LL;
int cnt[100001];
int main() {
	int N;
	cin >> N;
	rep(i, N) {
		int A;
		cin >> A;
		cnt[A]++;
	}
	bool OK = 1;
	if (N % 2 == 0) {
		for(int i=1;i<=N-1;i+=2) {
			if (cnt[i] != 2) {
				OK = 0;
				break;
			}
		}
	}
	else {
		for(int i=2;i<=N-1;i+=2) {
			if (cnt[i] != 2) {
				OK = 0;
				break;
			}
		}
		if (cnt[0] != 1) OK = 0;
	}
	if (OK) {
		LL ans = 1;
		rep(i, N / 2) {
			ans = (ans * 2) % MOD;
		}
		cout << ans << endl;
	}
	else {
		cout << 0 << endl;
	}
}

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