Submission #1695273

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Source Code Expand

#include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<cmath>
#include<vector>
#include<utility>
#include<stack>
#include<queue>
#include<list>
#include<bitset>

#define FOR(i, a, b) for(int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for(int i=(a);i>=(b);i--)
#define MOD 1000000007
#define INF 1000000000

using namespace std;

int main(void) {
	int n;
	int count = 0;
	int point = 0;
	long long int total = 1;
	int a[100001];

	cin >> n;
	FOR(i, 1, n) {
		cin >> a[i];
	}
	sort(a, a + n + 1);
	if (n % 2 == 0) {
		point = 1;
		FOR(i, 1, n) {
			if (a[i] == point&&a[i + 1] == point) {
				count++;
				point += 2;
				i++;
			}
			else {
				count = 0;
				break;
			}
		}
	}
	else {
		point = 0;
		if (a[1] == point) {
			point = 2;
			FOR(i, 2, n) {
				if (a[i] == point&&a[i + 1] == point) {
					count++;
					point += 2;
					i++;
				}
				else {
					count = 0;
					break;
				}
			}
		}
		else {
			count = 0;
		}
	}
	FOR(i, 1, count) {
		total *= 2;
		if (total > MOD) {
			total %= MOD;
		}
	}
	if (count == 0) {
		total = 0;
	}
	cout << total << endl;
	return 0;
}

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