Submission #261841

#TimeUsernameProblemLanguageResultExecution timeMemory
261841tko919Boat (APIO16_boat)C++17
100 / 100
629 ms4552 KiB
#define _USE_MATH_DEFINES #include <bits/stdc++.h> using namespace std; //template #define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++) #define ALL(v) (v).begin(),(v).end() typedef long long int ll; const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12; template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;} template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;} //end template<unsigned mod=1000000007>struct fp { int v; static unsigned get_mod(){return mod;} int inv() const{ int tmp,a=v,b=mod,x=1,y=0; while(b)tmp=a/b,a-=tmp*b,swap(a,b),x-=tmp*y,swap(x,y); if(x<0){x+=mod;} return x; } fp():v(0){} fp(ll x):v(x>=0?x%mod:mod+(x%mod)){} fp operator-()const{return fp(-v);} fp pow(ll t){fp res=1,b=*this; while(t){if(t&1)res*=b;b*=b;t>>=1;} return res;} fp& operator+=(const fp& x){if((v+=x.v)>=(int)mod)v-=mod; return *this;} fp& operator-=(const fp& x){if((v+=mod-x.v)>=(int)mod)v-=mod; return *this;} fp& operator*=(const fp& x){v=ll(v)*x.v%mod; return *this;} fp& operator/=(const fp& x){v=ll(v)*x.inv()%mod; return *this;} fp operator+(const fp& x)const{return fp(*this)+=x;} fp operator-(const fp& x)const{return fp(*this)-=x;} fp operator*(const fp& x)const{return fp(*this)*=x;} fp operator/(const fp& x)const{return fp(*this)/=x;} bool operator==(const fp& x)const{return v==x.v;} bool operator!=(const fp& x)const{return v!=x.v;} }; using Fp=fp<>; template<typename T>struct factorial { vector<T> Fact,Finv,Inv; factorial(int maxx){ Fact.resize(maxx); Finv.resize(maxx); Inv.resize(maxx); Fact[0]=Fact[1]=Finv[0]=Finv[1]=Inv[1]=1; rep(i,2,maxx){Fact[i]=Fact[i-1]*i;} Finv[maxx-1]=Fact[maxx-1].inv(); for(int i=maxx-1;i>=2;i--){Finv[i-1]=Finv[i]*i; Inv[i]=Finv[i]*Fact[i-1];} } T fact(int n,bool inv=0){if(inv)return Finv[n];else return Fact[n];} T inv(int n){return Inv[n];} T nPr(int n,int r){if(n<0||n<r||r<0)return Fp(0);else return Fact[n]*Finv[n-r];} T nCr(int n,int r){if(n<0||n<r||r<0)return Fp(0);else return Fact[n]*Finv[r]*Finv[n-r];} }; Fp dp[510][1010],c[1010][510]; factorial<Fp> fact(1010); int main(){ int n; cin>>n; vector<int> a(n),b(n),vs={0,inf}; rep(i,0,n){ cin>>a[i]>>b[i]; b[i]++; vs.push_back(a[i]); vs.push_back(b[i]); } sort(ALL(vs)); vs.erase(unique(ALL(vs)),vs.end()); int m=vs.size(); rep(i,0,n){ a[i]=lower_bound(ALL(vs),a[i])-vs.begin(); b[i]=lower_bound(ALL(vs),b[i])-vs.begin(); } //precalc rep(i,0,m-1){ c[i][0]=1; rep(j,0,n)c[i][j+1]=c[i][j]*(vs[i+1]-vs[i]+j)*fact.inv(j+1); } Fp res; rep(i,0,n){ rep(j,a[i],b[i]){ int cnt=0; for(int k=i;k;k--){ if(a[k]<=j and j<b[k])cnt++; dp[i][j+1]+=dp[k-1][j]*c[j][cnt]; } if(a[0]<=j and j<b[0])cnt++; dp[i][j+1]+=c[j][cnt]; } rep(j,0,m-1)dp[i][j+1]+=dp[i][j]; res+=dp[i][m-1]; } cout<<res.v<<endl; return 0; }
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