#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 T[2*N]; void Update(int i,int x){for(;i<=2*N;i+=i&-i)T[i]+=x;} int Get(int i){int x=0;for(;i>=1;i-=i&-i)x+=T[i];return x;} int Get(int l,int r){return Get(r)-Get(l-1);} 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){ if(Get(L[j],R[j])==0)res=(res<<1)%mod; Update(R[j],1); } } 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;} } 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:18:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   18 |     scanf("%i",&n);
      |     ~~~~~^~~~~~~~~
port_facility.cpp:20:22: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   20 |         int x,y;scanf("%i%i",&x,&y);
      |                 ~~~~~^~~~~~~~~~~~~~