# | Time | Username | Problem | Language | Result | Execution time | Memory |
---|---|---|---|---|---|---|---|
30763 | PrOAhMeT | Boat (APIO16_boat) | C++14 | 0 ms | 0 KiB |
This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define LL long long
#define st first
#define nd second
#define endl '\n'
using namespace std;
const int MAXN=505;
LL dp[MAXN][MAXN*2],n,a[MAXN],b[MAXN],mod=1e9+7;
vector<LL> po;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cin>>n;
for(int i=1;i<=n;++i) {
cin>>a[i]>>b[i];
po.pb(a[i]);
po.pb(b[i]);
}
po.pb(0);
po.pb(2e9);
sort(po.begin(),po.end());
po.resize(unique(po.begin(),po.end())-po.begin());
for(int i=1;i<=n;++i) {
a[i]=lower_bound(po.begin(),po.end(),a[i])-po.begin();
b[i]=lower_bound(po.begin(),po.end(),b[i])-po.begin();
}
for(int j=0;j<po.size()+2;++j)
dp[n+1][j]=1;
for(int i=n;i>=1;--i) {
for(int j=0;j<po.size();++j) {
dp[i][j]=dp[i+1][j];
if(j<=a[i]) {
dp[i][j]+=dp[i+1][a[i]+1];
if(dp[i][j]>=mod)
dp[i][j]-=mod;
}
for(int k=max(a[i]+1,j);k<=b[i];++k) {
dp[i][j]=(dp[i][j]+(1LL*(po[k]-po[k-1])*dp[i+1][k+1])%mod);
if(dp[i][j]>=mod)
dp[i][j]-=mod;
//cout<<"doing "<<i<<" "<<k<<" "<<po[k]-po[k-1]<<" "<<dp[i+1][k]<<endl;
}
//cout<<i<<" "<<j<<" "<<po[j]<<" "<<dp[i][j]<<" "<<a[i]<<" "<<b[i]<<endl;
}
}
cout<<(dp[1][1]-1+mod)%mod<< endl;
}