Submission #1518383

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Source Code Expand

#include <bits/stdc++.h>
#include <math.h>
#define uint unsigned long long
#define ll long long
#define db double
#define ls rt << 1
#define rs rt << 1 | 1
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define X first
#define Y second
#define pcc pair<char, char>
#define vi vector<int>
#define vl vector<ll>
#define rep(i, x, y) for(int i = x; i <= y; i ++)
#define rrep(i, x, y) for(int i = x; i >= y; i --)
#define ept 1e-9

using namespace std;
inline int read()
{
    int x = 0, f = 1; char ch = getchar();
    while (ch < '0' || ch > '9') { if (ch == '-') f = -1; ch = getchar(); }
    while (ch >= '0' && ch <= '9') { x = x * 10 + ch - '0'; ch = getchar(); }
    return x * f;
}
const int mod = 1e9 + 7;
const int N = 100010;
int n;
int a[N], po[N];

int main()
{
    po[0] = 1;
    for(int i = 1; i < N; i++)
	    po[i] = po[i - 1] * 2 % mod;

    n = read();
    rep(i, 0, n - 1) a[i] = read();

    sort(a, a + n);

    if(n % 2)
    {
    	rep(i, 0, n - 1)
            if(a[i] != ((i + 1) / 2) * 2)
            {
                printf("0");
                return 0;
            }
    }
    else
    {
    	rep(i, 0, n - 1)
            if(a[i] != (i / 2) * 2 + 1)
            {
                printf("0");
                return 0;
            }
    }
    printf("%d", po[n / 2]);
    return 0;
}

Submission Info

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