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
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
#include <bits/stdc++.h>


using namespace std;


const int MOD = 1000 * 1000 * 1000 + 7;


int add(int x, int y) {
    x += y;
    if (x >= MOD) {
        x -= MOD;
    }

    return x;
}

struct PointUpdateTree {
    typedef int val_t;

    val_t getValInit(int i) { return 0; }
    val_t combine(const val_t &a, const val_t &b) { return add(a, b); }

    int p = 1;
    vector <val_t> tree;

    PointUpdateTree(int n) {
        while (p < n) p *= 2;

        int m = 2 * p - 1;
        tree.resize(m);

        for (int i = p - 1; i < m; i++) {
            tree[i] = getValInit(i - p + 1);
        }

        for (int i = p - 2; i >= 0; i--) {
            tree[i] = combine(tree[2 * i + 1], tree[2 * i + 2]);
        }
    }

    int par(int x) { return (x - 1) / 2; }

    void update(int l, val_t v) {
        l += p - 1;
        tree[l] = v;

        while (l > 0) {
            l = par(l);
            tree[l] = combine(tree[2 * l + 1], tree[2 * l + 2]);
        }
    }

    val_t query(int l, int r) {
        if (l > r) {
            return 0;
        }

        l += p - 1; r += p - 1;

        if (l == r) {
            return tree[l];
        }

        val_t ans = combine(tree[l], tree[r]);
        while (par(l) != par(r)) {
            if (l % 2 == 1) ans = combine(ans, tree[l + 1]);
            if (r % 2 == 0) ans = combine(ans, tree[r - 1]);

            l = par(l);
            r = par(r);
        }

        return ans;
    }
};

int solve(int n, vector <int> &arr) {
    vector <int> pref(n + 1, 0);
    for (int i = 1; i <= n; i++) {
        pref[i] = add(pref[i - 1], arr[i - 1]);
    }

    vector <pair<int,int>> remAndPos(n + 1);
    for (int i = 0; i <= n; i++) {
        remAndPos[i] = {pref[i], i};
    }

    auto remAndPosSorted = remAndPos;
    sort(remAndPosSorted.begin(), remAndPosSorted.end());

    vector <vector<pair<int,int>>> remForParity(2);
    for (auto &e : remAndPosSorted) {
        remForParity[e.first % 2].push_back(e);
    }

    vector <PointUpdateTree> dpForParity;
    for (int par = 0; par <= 1; par++) {
        dpForParity.emplace_back(remForParity[par].size());
    }

    vector <int> dp(n + 1, 0);
    dp[0] = 1;

    auto recordDP = [&](int i) {
        int par = pref[i] % 2;
        int idx = lower_bound(
            remForParity[par].begin(), remForParity[par].end(), remAndPos[i]
        ) - remForParity[par].begin();

        dpForParity[par].update(idx, dp[i]);
    };

    recordDP(0);

    for (int i = 1; i <= n; i++) {
        int par = pref[i] % 2;
        int parNeg = 1 - par;

        pair <int,int> e = {pref[i], n + 1};

        int jHigh = upper_bound(
            remForParity[par].begin(), remForParity[par].end(), e
        ) - remForParity[par].begin() - 1;
        dp[i] = add(dp[i], dpForParity[par].query(0, jHigh));

        int jLow = upper_bound(
            remForParity[parNeg].begin(), remForParity[parNeg].end(), e
        ) - remForParity[parNeg].begin();
        dp[i] = add(dp[i], dpForParity[parNeg].query(jLow, (int) remForParity[parNeg].size() - 1));

        recordDP(i);
    }

    return dp[n];
}

int main() {
    ios_base::sync_with_stdio(false);

    int n;
    cin >> n;

    vector <int> arr(n);
    for (int &ai : arr) {
        cin >> ai;
    }

    cout << solve(n, arr);

    return 0;
}