1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
#include<bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define ST first
#define ND second
#define SIZE(a) ((int)a.size())

const int mod = 1e9+7;

struct Tree {
    static const int size = 1<<20;
    int shift = 1<<19;
    vector<int> t;

    Tree() : t(size) {}
    
    void add(int id, int value) {
        id+=shift;
        t[id] = (t[id]+value)%mod;
        id/=2;
        while(id) {
            t[id] = (t[2*id] + t[2*id+1])%mod;
            id/=2;
        }
    }

    ll sum(int left, int right) {
        if(left > right) {
            return 0;
        }
        left += shift;
        right += shift;
        ll res = t[left];
        if(left < right) {
            res += t[right];
        }
        while(left/2 != right/2) {
            if(left % 2 == 0) {
                res += t[left+1];
            }
            if(right %2 == 1) {
                res += t[right-1];
            }
            left/=2;
            right/=2;
        }
        return res;
    }
};

int main() {
    ios_base::sync_with_stdio(0);
    int n;
    cin >> n;
    vector<int> a(n);

    ll sum = 0;
    vector<int> values;
    values.push_back(sum);
    for(int &a_i : a) {
        cin >> a_i;
        sum = (sum+a_i)%mod;
        values.push_back(sum);
    }

    sort(values.begin(), values.end());
    map<int, int> mapping;
    int num = 0;
    int prev_value = -1;
    for(int value : values) {
        if(prev_value != value) {
            mapping[value] = num++;
        }
        prev_value = value;
    }
    
    sum = 0;
    Tree even, odd;
    even.add(0, 1);
    ll value = 0;
    for(int i=0; i < n; i++) {
        sum = (sum+a[i])%mod;
        int id = mapping[sum];
        if(sum%2 == 1) {
            value = odd.sum(0, id) + even.sum(id+1, num-1);
            value%=mod;
            odd.add(id, value);
        } else {
            value = even.sum(0, id) + odd.sum(id+1, num-1);
            value%=mod;
            even.add(id, value);
        }
        // cout << value << "\n";
    }
    cout << value << "\n";
}