I. Improve SPAM

题意：

DAG上从1号点到其他终止点的路径方案数

AC代码：

const int N = 2020;
const ll mod = 1e9 + 7;
vector<ll> edge[N];
ll n, m, dp[N], cnt = 0, ans = 0;

ll dfs(ll cur)
{
  if (dp[cur] != -1)
    return dp[cur];
  if (cur > m)
  {
    cnt++;
    dp[cur] = 1;
    return dp[cur];
  }
  ll sum = 0;
  for (auto x : edge[cur])
    sum = ((dfs(x) % mod) + sum) % mod;
  dp[cur] = sum;
  return sum;
}

int main()
{
  rep(i, 0, N - 1)
    dp[i] = -1;
  sldd(n, m);
  rep(i, 1, m)
  {
    ll x;
    sld(x);
    while (x--)
    {
      ll y;
      sld(y);
      edge[i].pb(y);
    }
    sort(edge[i].begin(), edge[i].end());
  }
  ll ans = dfs(1);
  pldd(ans, cnt);
  return 0;
}