Submission #970768

#	Time	Username	Problem	Language	Result	Execution time	Memory
970768		vjudge1	Boat (APIO16_boat)	C++14	9 / 100	4 ms	2648 KiB

boat

#include<bits/stdc++.h>

using namespace std;

const int N=510, mod=1e9+7;
int fact[N*2], invfact[N*2];

int binpow(int x, int y){
   int t=1;
   while (y){
      if (y&1) t=1ll*t*x%mod;
      x=1ll*x*x%mod;
      y>>=1;
   }
   return t;
}

void precalc(){
   fact[0]=1;
   for (int i=1; i<N*2; ++i) fact[i]=1ll*fact[i-1]*i%mod;
   invfact[N*2-1]=binpow(fact[N*2-1], mod-2);
   for (int i=N*2-2; i>=0; --i) invfact[i]=1ll*invfact[i+1]*(i+1)%mod;
}

int C(int n, int k){
   if (n<0 || k<0 || n<k) return 0;
   return 1ll*fact[n]*invfact[k]%mod*invfact[n-k]%mod;
}

int f[N][N*2], n, a[N], b[N];
vector<int> vals;

int32_t main(){
   ios_base::sync_with_stdio(false);
   cin.tie(nullptr);
   precalc();
   vals.push_back(-1);
   cin >> n;
   for (int i=1; i<=n; ++i) cin >> a[i] >> b[i], vals.push_back(a[i]), vals.push_back(++b[i]);
   sort(vals.begin(), vals.end());
   vals.resize(unique(vals.begin(), vals.end())-vals.begin());
   for (int i=1; i<=n; ++i){
      a[i]=lower_bound(vals.begin(), vals.end(), a[i])-vals.begin();
      b[i]=lower_bound(vals.begin(), vals.end(), b[i])-vals.begin();
   }
   for (int i=0; i<(int)vals.size(); ++i) f[0][i]=1;
   for (int i=1; i<=n; ++i){
      for (int j=a[i]; j<b[i]; ++j){
         f[i][j]=f[i][j-1];
         for (int k=i-1; k>=0; --k){
            f[i][j]=(f[i][j]+1ll*f[k][j-1]*C(vals[j+1]-vals[j], i-k))%mod;
            if (j<a[k] || b[k]<=j) break;
         }
      }
      for (int j=b[i]; j<(int)vals.size(); ++j) f[i][j]=f[i][j-1];
      for (int j=0; j<(int)vals.size(); ++j) f[i][j]=(f[i][j]+f[i-1][j])%mod;
   }
   cout << (f[n][(int)vals.size()-1]+mod-1)%mod << '\n';
   return 0;
}

• Subtask 1: 9 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42