#include <bits/stdc++.h> using namespace std; #define fi first #define se second #define pb push_back #define ll long long const int N=1e6+50,mod=1e9+7; int n,ev[2*N]; int L[N],R[N]; ll res=1; vector<int>a,b; set<int>A,B; int main(){ scanf("%i",&n); for(int i=1;i<=n;i++){ int x,y;scanf("%i%i",&x,&y); ev[x]=i,ev[y]=-i; L[i]=x,R[i]=y; } for(int i=1;i<=2*n;i++){ int j=abs(ev[i]); if(ev[i]>0){ int bul=0; if(A.empty()||*A.begin()>R[j]){ a.pb(j),A.insert(R[j]); bul++; } if(B.empty()||*B.begin()>R[j]){ if(bul==0)b.pb(j),B.insert(R[j]); bul++; } if(bul==0){res=0;break;} if(bul==2)res=(res<<1)%mod; } else{ if(a.back()==j){ a.pop_back(); A.erase(R[j]); } else if(b.back()==j){ b.pop_back(); B.erase(R[j]); } else{res=0;break;} } } printf("%lld\n",res); return 0; }

port_facility.cpp: In function 'int main()':
port_facility.cpp:14:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   14 |     scanf("%i",&n);
      |     ~~~~~^~~~~~~~~
port_facility.cpp:16:22: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   16 |         int x,y;scanf("%i%i",&x,&y);
      |                 ~~~~~^~~~~~~~~~~~~~