#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define int ll
#define MP make_pair
#define pb push_back
#define F first
#define S second
#define pii pair<int,int>
#define REP(i,a,b) for(int i=a; i<b; i++)
const int MX=5e2+3, mod=1e9+7;
int n, m, dp[10][MX*2][2*MX], l[MX], r[MX], num[2*MX], p[MX*2];
map<int,int> mark;
vector<int> vec;
int32_t main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
REP(i,1,MX*2) p[i]=pw(i,mod-2);
cin>>n;
REP(i,0,n){
cin>>l[i]>>r[i];
r[i]++;
if(!mark[l[i]]) mark[l[i]]=1, vec.pb(l[i]);
if(!mark[r[i]]) mark[r[i]]=1, vec.pb(r[i]);
}
m=vec.size();
sort(vec.begin(), vec.end());
int mm=0;
dp[mm][0][0]=1;
REP(j,1,m){
dp[mm][j][0]=dp[mm][j-1][0]+dp[mm][j-1][1];
if(l[0]<vec[j] && r[0]>=vec[j]) dp[mm][j][1]=(vec[j]-vec[j-1])%mod, num[j]++;
}
REP(i,1,n){
mm^=1;
REP(j,1,m){
dp[mm][j][0]=0;
if(j>1) REP(w,0,num[j-1]+1) dp[mm][j][0]=(dp[mm][j-1][w]+dp[mm][j][0])%mod;
else dp[mm][j][0]=1;
int flg=0, cnt=vec[j]-vec[j-1];
if(l[i]<vec[j] && r[i]>=vec[j]) flg=1, num[j]++;
REP(w,1,num[j]+1){
dp[mm][j][w]=dp[mm^1][j][w];
if(flg) dp[mm][j][w]=((ll)dp[mm][j][w] + (ll)dp[mm^1][j][w-1] * (cnt-w+1) %mod * p[w]%mod )%mod;
}
}
}
int sum=0;
REP(w,0,MX*2) sum=(sum+dp[mm][m-1][w])%mod;
cout<<sum-1<<endl;
return 0;
}
Compilation message
boat.cpp: In function 'int32_t main()':
boat.cpp:20:21: error: 'pw' was not declared in this scope
REP(i,1,MX*2) p[i]=pw(i,mod-2);
^~
boat.cpp:20:21: note: suggested alternative: 'p'
REP(i,1,MX*2) p[i]=pw(i,mod-2);
^~
p
