GRAPH (VOI 2022)

#define task "GRAPH"
#include <iostream>
#include <cstdio>

using namespace std;

using ll = long long;
using ld = long double;

constexpr int N = 2e3 + 5;
constexpr int mod = 1e9 + 7;
int a[N], n, b;
int dp[N][N], g[N][N];

void Read()
{
    cin >> n >> b;

    for (int i = 1; i <= n; ++i)
        cin >> a[i];
}

void Sub_3()
{
    dp[n + 1][0] = 1;

    for (int i = n; i; --i)
        for (int j = 0; j <= n - i + 1; ++j)
        {
            if (a[i] == -1)
            {
                for (int t = 0; t <= i - 1; ++t)
                    if (j >= (t > 0) && t + j - (t > 0) <= b)
                        (dp[i][j] += dp[i + 1][j - (t > 0)]) %= mod;
            }
            else
            {
                if (j >= (a[i] > 0) && a[i] + j - (a[i] > 0) <= b)
                    (dp[i][j] += dp[i + 1][j - (a[i] > 0)]) %= mod;
            }

            g[i][j] = ((j == 0 ? 0 : g[i][j - 1]) + dp[i][j]) % mod;
        }

    int ans(0);

    for (int i = 0; i <= n; ++i)
        (ans += dp[1][i]) %= mod;

    cout << (ans + mod) % mod;
}

void Solve()
{
    dp[n + 1][0] = 1;

    for (int i = n; i; --i)
    {
        for (int j = 0; j <= n - i + 1 && j <= b; ++j)
        {
            if (a[i] == -1)
            {
                int t = min(i - 1, b);

                if (j == 0)
                    t = min(t, 0);
                else if (j == b)
                    t = min(t, 1);
                else
                    t = min(t, b - j + 1);

                //for (int t = 0; t <= i - 1 && j >= (t > 0) && t + j - (t > 0) <= b; ++t)
                //    (dp[i][j] += dp[i + 1][j - (t > 0)]) %= mod;

                dp[i][j] = (dp[i + 1][j] + 1ll * dp[i + 1][j - 1] * t % mod) % mod;
            }
            else
            {
                if (j >= (a[i] > 0) && a[i] + j - (a[i] > 0) <= b)
                    (dp[i][j] += dp[i + 1][j - (a[i] > 0)]) %= mod;
            }
        }

        for (int j = 0; j <= n; ++j)
            g[i][j] = ((j == 0 ? 0 : g[i][j - 1]) + dp[i][j]) % mod;
    }

    int ans(0);

    for (int i = 0; i <= n; ++i)
        (ans += dp[1][i]) %= mod;

    cout << (ans + mod) % mod;
}

int32_t main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    if (fopen(task ".INP", "r"))
    {
        freopen(task ".INP", "r", stdin);
        freopen(task ".OUT", "w", stdout);
    }

    Read();
    Solve();
}