#include <bits/stdc++.h> //#define int long long #define pii pair<int, int> #define fi first #define se second #define vi vector <int> #define pq priority_queue #define MASK(i) (1ll<<(i)) #define BIT(x, i) (((x) >> (i)) & 1) #define x0 ___x0 #define y0 ___y0 #define div ___div #define next ___next #define prev ___prev #define left ___left #define right ___right #define pos pisosi #define pb push_back #define pf push_front using namespace std; const int mod = 1e9+7; void add (int &a, const int&b){ a+=b; if (a>=mod) a-=mod; } void sub (int&a, const int&b){ a-=b; if (a<0) a+=mod; } void mul (int&a, const int&b){ a = 1ll*a*b%mod; } template<class X, class Y> bool minimize(X &x, const Y&y){ if (x<=y) return false; else{ x = y; return true; } } template<class X, class Y> bool maximize (X &x, const Y&y){ if (x>=y) return false; else{ x = y; return true; } } ///////////////////////////////////////////////////////////////////////////////// //// dang nhap ham //#ifndef davele // //#endif // davele // //// chay thu ham main: // //#ifdef davele // //#endif // davele //////////////////////////////////////////////////////////////////////////// //const int lim = , limit = , inf = ; const string name = "boat"; const int lim = 1050, limit = lim+5; int powe (int coso, int somu){ int ret = 1; while (somu>0){ if (somu&1) mul (ret, coso); mul (coso, coso); somu>>=1; } return ret; } vector <int> ds; int L[limit], R[limit], numrange; int sum[limit][limit]; vector <int> inside[limit]; int dp[limit][limit]; int sumdp[limit][limit]; int prep[limit][limit]; int n; int inv[limit]; int C[limit][limit]; void compress(){ ds.pb(-1); for (int i=1; i<=n; i++){ ds.pb(L[i]); ds.pb(R[i]+1); } sort (ds.begin(), ds.end()); ds.erase (unique(ds.begin(), ds.end()), ds.end()); ds.pb(ds.back()+1); // range[i] = [ds[i]; ds[i+1]-1] // numrange = ds.size()-2; // for (int i=1; i<=numrange; i++) cerr<<ds[i]<<" "<<ds[i+1]<<"\n"; } void process(){ compress(); // for (int i=1; i<=n; i++){ for (int j=1; j<=numrange; j++){ sum[i][j] = sum[i-1][j]; // cerr<<L[i]<<" "<<R[i]<<" "<<" "<<j<<"\n"; if (L[i]<=ds[j] && ds[j+1]-1<=R[i]){ inside[i].pb(j); // cerr<<i<<" "<<j<<"\n"; sum[i][j]++; } } } // sum[i][j] : xet den nguoi thu i, co bao nhieu team co the nam trong range j // C[k][n] for (int i=0; i<=lim; i++) C[0][i] = 1; for (int i=1; i<=lim; i++) for (int j=1; j<=i; j++){ C[j][i] = (C[j-1][i-1] + C[j][i-1])%mod; } for (int i=1; i<=lim; i++) inv[i] = powe (i, mod-2); // prep[kind][cnt] : so cach chon phu hop sao cho voi cnt team thi team cuoi cung chac chan // duoc chon // prep[kind][cnt] = sum (C(k-1, cnt-1)*C(k, lenrange)) voi k chay tu 1 den min(cnt, lenrange) for (int kind = 1; kind<=numrange; kind++){ int lenrange = ds[kind+1]-ds[kind]; for (int cnt = 1; cnt<=sum[n][kind]; cnt++){ int mx = min(cnt, lenrange); int tu = 1, mau = 1; for (int chose = 1; chose<=mx; chose++){ mul (tu, lenrange-chose+1); mul (mau, inv[chose]); add (prep[kind][cnt], 1ll*C[chose-1][cnt-1]*tu%mod*mau%mod); } // cerr<<kind<<" "<<cnt<<" "<<prep[kind][cnt]<<"\n"; } } // dp[i][j] : den vi tri i, so cach chon sao cho o group i co chon nguoi o range j int ret = 0; dp[0][0] = 1; for (int i=0; i<=lim; i++) sumdp[0][i] = 1; for (int i=1; i<=n; i++){ for (int x:inside[i]){ for (int j=0; j<i; j++){ add (dp[i][x], 1ll*sumdp[j][x-1]*prep[x][sum[i][x]-sum[j][x]]%mod); } add (ret, dp[i][x]); } for (int j=1; j<=numrange; j++) sumdp[i][j] = (sumdp[i][j-1]+dp[i][j])%mod; } cout<<ret; } signed main(){ ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); // if (fopen((name+".inp").c_str(), "r")){ freopen ((name+".inp").c_str(), "r", stdin); freopen ((name+".out").c_str(), "w", stdout); } // cin>>n; for (int i=1; i<=n; i++){ cin>>L[i]>>R[i]; } process(); }

boat.cpp: In function 'int main()':
boat.cpp:169:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  169 |         freopen ((name+".inp").c_str(), "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
boat.cpp:170:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  170 |         freopen ((name+".out").c_str(), "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~