Submission #1112947

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Source Code Expand

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <vector>
#include <iostream>
#include <set>
#include <map>
using namespace std;
typedef long long ll;

int N;
int A[100005];
ll MOD = 1e9+7;

int main(int argc, char const *argv[]) {
	cin >> N;
	vector<int> v(N);

	for (int i = 0; i < N; i++) {
		cin >> v[i];
	}
	sort(v.begin(), v.end());

	if (N % 2 == 0) {
		int check = 1;
		for (int i = 0; i < N; i++) {
			if (i % 2 == 0 && v[i] == check) {
				continue;
			}
			else if (i % 2 == 1 && v[i] == check) {
				check += 2;
				continue;
			}
			else {
				cout << "0" << endl;
				return 0;
			}
		}
	}

	else {
		if (v[0] != 0) {
			cout << "0" << endl;
			return 0;
		}
		int check = 2;
		for (int i = 1; i < N; i++) {
			if (i % 2 == 1 && v[i] == check) {
				continue;
			}
			else if (i % 2 == 0 && v[i] == check) {
				check += 2;
				continue;
			}
			else {
				cout << "0" << endl;
				return 0;
			}
		}
	}		

	ll res = 1;

	for (int i = 0; i < N/2; i++) {
		res *= 2;
		res %= MOD;
	}
	cout << res << endl;
	
	return 0;
}

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