#pragma GCC target("avx2") #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") #include #include // cout, endl, cin #include // string, to_string, stoi #include // vector #include // min, max, swap, sort, reverse, lower_bound, upper_bound #include // pair, make_pair #include // tuple, make_tuple #include // int64_t, int*_t #include // printf #include // map #include // queue, priority_queue #include // set #include // stack #include // deque #include // unordered_map #include // unordered_set #include // bitset #include // isupper, islower, isdigit, toupper, tolower #include #include #include using namespace std; using namespace atcoder; #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define repi(i, a, b) for (int i = (int)(a); i < (int)(b); i++) typedef long long ll; typedef unsigned long long ull; const ll inf=1e18; using graph = vector > ; using P= pair; using vi=vector; using vvi=vector; using vll=vector; using vvll=vector; using vp=vector

; using vvp=vector; using vd=vector; using vvd =vector; //string T="ABCDEFGHIJKLMNOPQRSTUVWXYZ"; //string S="abcdefghijklmnopqrstuvwxyz"; //g++ main.cpp -std=c++17 -I . //cout < bool chmin(T& a, T b) { if (a > b) { a = b; return true; } else return false; } template bool chmax(T& a, T b) { if (a < b) { a = b; return true; } else return false; } // https://youtu.be/L8grWxBlIZ4?t=9858 // https://youtu.be/ERZuLAxZffQ?t=4807 : optimize // https://youtu.be/8uowVvQ_-Mo?t=1329 : division //ll mod =998244353; ll mod =1e9+7; struct mint { ll x; // typedef long long ll; mint(ll x=0):x((x%mod+mod)%mod){} mint operator-() const { return mint(-x);} mint& operator+=(const mint a) { if ((x += a.x) >= mod) x -= mod; return *this; } mint& operator-=(const mint a) { if ((x += mod-a.x) >= mod) x -= mod; return *this; } mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;} mint operator+(const mint a) const { return mint(*this) += a;} mint operator-(const mint a) const { return mint(*this) -= a;} mint operator*(const mint a) const { return mint(*this) *= a;} mint pow(ll t) const { if (!t) return 1; mint a = pow(t>>1); a *= a; if (t&1) a *= *this; return a; } // for prime mod mint inv() const { return pow(mod-2);} mint& operator/=(const mint a) { return *this *= a.inv();} mint operator/(const mint a) const { return mint(*this) /= a;} }; istream& operator>>(istream& is, const mint& a) { return is >> a.x;} ostream& operator<<(ostream& os, const mint& a) { return os << a.x;} // combination mod prime // https://www.youtube.com/watch?v=8uowVvQ_-Mo&feature=youtu.be&t=1619 struct combination { vector fact, ifact; combination(int n):fact(n+1),ifact(n+1) { //assert(n < mod); fact[0] = 1; for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i; ifact[n] = fact[n].inv(); for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i; } mint operator()(int n, int k) { if (k < 0 || k > n) return 0; if (n<0) return 0; return fact[n]*ifact[k]*ifact[n-k]; } mint p(int n, int k) { return fact[n]*ifact[n-k]; } } c(2000000); using vm=vector ; using vvm=vector ; struct edge{ int to; ll cost; edge(int to,ll cost) : to(to),cost(cost){} }; using ve=vector; using vve=vector; struct Compress{ vll a; map d,d2; int cnt; Compress() :cnt(0) {} void add(ll x){a.push_back(x);} void init(){ sets(a.begin(),a.end()); for(auto y:s)d[y]=cnt++; for(auto&y:a)y=d[y]; for(auto u:d)d2[u.second]=u.first; } ll to(ll x){return d[x];} //変換先 ll from(ll x){return d2[x];}//逆引き int size(){return cnt;} }; struct UnionFind { vector par, siz; UnionFind(int n) : par(n, -1) , siz(n, 1) { } int root(int x) { if (par[x] == -1) return x; else return par[x] = root(par[x]); } bool issame(int x, int y) { return root(x) == root(y); } bool unite(int x, int y) { x = root(x), y = root(y); if (x == y) return false; if (siz[x] < siz[y]) swap(x, y); par[y] = x; siz[x] += siz[y]; return true; } int size(int x) { return siz[root(x)]; } }; vll anss; void solve(int test){ int n; cin>> n; vi x(n+1),y(n+1); rep(i,n){ int t,c; cin >> t >> c; if(t)x[c]++; else y[c]++; } vvm dp(n+1,vm(n+1)); dp[0][0]=1; int tot=0; int tot2=0; vm kai(n+1,1); for(int i=1; i<=n; i++)kai[i]=kai[i-1]*i; rep(i,n){ rep(j,n+1){ mint now=dp[i][j]; if(!now.x)continue; if(y[i+1]){ { if(j+x[i+1]<=n)dp[i+1][j+x[i+1]]+=now*c(i-(tot-j)-tot2,y[i+1])*kai[y[i+1]]; if(j+x[i+1]-1<=n && j+x[i+1]-1>=0)dp[i+1][j+x[i+1]-1]+=now*c(i-(tot-j)-tot2,y[i+1])*(j+x[i+1])*kai[y[i+1]]; } { if(j+x[i+1]<=n)dp[i+1][j+x[i+1]]+=now*c(i-(tot-j)-tot2,y[i+1]-1)*kai[y[i+1]]; } } else { if(j+x[i+1]<=n)dp[i+1][j+x[i+1]]+=now; if(j+x[i+1]-1<=n && j+x[i+1]-1>=0)dp[i+1][j+x[i+1]-1]+=now*(j+x[i+1]); } } tot+=x[i+1]; tot2+=y[i+1]; } mint ans=dp[n][0]; cout << ans << endl; } //g++ main.cpp -std=c++17 -I . int main(){cin.tie(0);ios::sync_with_stdio(false); int t=1;//cin >> t; rep(test,t)solve(test); for(auto u:anss)cout << u << endl; }