#include<bits/stdc++.h>
using namespace std;
#define maxn 1005
#define int long long
const int mod=1e9+7;
int power(int a,int n){
int res=1;
while(n){
if(n&1) res=(res*a)%mod;
a=(a*a)%mod;n>>=1;
}
return res;
}
vector<int> x;
int n,l[maxn],r[maxn],dp[maxn][maxn],divs[maxn];
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);cout.tie(NULL);
cin >> n;divs[0]=1;
for(int i=1;i<=n;i++){
cin >> l[i] >> r[i];
divs[i]=divs[i-1]*power(i,mod-2);
l[i]-=i;r[i]-=i;r[i]++;
x.push_back(l[i]);x.push_back(r[i]);
}
sort(x.begin(),x.end());
x.erase(unique(x.begin(),x.end()),x.end());
int m=(int)x.size();
for(int i=1;i<=n;i++){
l[i]=lower_bound(x.begin(),x.end(),l[i])-x.begin()+1;
r[i]=lower_bound(x.begin(),x.end(),r[i])-x.begin();
}
for(int i=0;i<=m;i++) dp[0][i]=1;
for(int i=1;i<=n;i++){
for(int j=1;j<m;j++){
dp[i][j]=dp[i][j-1];
if(j<l[i] || j>r[i]) continue;
int len=x[j]-x[j-1],mul=1;
for(int k=i-1;k>=0;k--){
mul=mul*(len+i-k-1)%mod*divs[i-k]%mod;
dp[i][j]=(dp[i][j]+dp[k][j-1]*mul)%mod;
}
}
for(int j=0;j<m;j++) dp[i][j]=(dp[i][j]+dp[i-1][j])%mod;
}
cout << (dp[n][m-1]+mod-1)%mod << '\n';
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
6 ms |
4308 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
6 ms |
4308 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
4 ms |
852 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
6 ms |
4308 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
