#include <bits/stdc++.h> using namespace std; #define FOR(i, a, b) for(int i = a; i <= b; i++) #define FOD(i, a, b) for(int i = a; i >= b; i--) #define fi first #define se second #define ll long long #define db double #define ii pair<int,int> #define pb push_back #define MASK(i) (1LL << i) #define sq(i) (1LL * (i) * (i)) #define task "task" const ll INF = 1e18; const int inf = 1e9; const int N = 1e6 + 4; const int mod = 1e9 + 7; int mul(int a, int b) { return 1LL * a * b % mod; } int n; ii a[N]; struct Dsu { int cc; int root[N], sze[N], h[N]; void init() { cc = n; FOR(i, 1, n) { h[i] = 0; root[i] = i; sze[i] = 1; } } ii anc(int u) { if(u == root[u]) return {u, 0}; ii tmp = anc(root[u]); root[u] = tmp.fi; h[u] += tmp.se; return {root[u], h[u]}; } bool join(int u, int v) { ii ru = anc(u); ii rv = anc(v); if(ru.fi == rv.fi) { if((ru.se + rv.se) % 2 == 0) return true; return false; } cc--; if(sze[ru.fi] < sze[rv.fi]) swap(ru, rv); root[rv.fi] = ru.fi; sze[ru.fi] += sze[rv.fi]; h[rv.fi] = (rv.se + ru.se + 1) % 2; return false; } } dsu; vector<int> cur; int idx[2 * N]; struct Event { int p, t, id; bool operator < (const Event &b) const { return p < b.p; } }; vector<Event> ev; int binpow(int a, int b) { if(b == 0) return 1; int tmp = binpow(a, b / 2); if(b & 1) return mul(mul(tmp, tmp), a); return mul(tmp, tmp); } void solve() { FOR(i, 1, n) { ev.pb({a[i].fi, 0, i}); ev.pb({a[i].se, 1, i}); } sort(ev.begin(), ev.end()); dsu.init(); for(auto x : ev) { if(x.t == 0) cur.pb(x.p); else { vector<int>::iterator it = lower_bound(cur.begin(), cur.end(), a[x.id].fi); int st = it - cur.begin() + 1; for(; st < cur.size(); st++) { if(dsu.join(idx[cur[st]], x.id)) { cout << 0 << '\n'; return; } } cur.erase(it); } } cout << binpow(2, dsu.cc) << '\n'; } signed main() { if(fopen(task".inp", "r")) { freopen(task".inp", "r", stdin); //freopen(task".out", "w", stdout); } ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); int tc = 1; // cin >> tc; while(tc--) { cin >> n; FOR(i, 1, n) { cin >> a[i].fi >> a[i].se; idx[a[i].fi] = i; } solve(); } }

port_facility.cpp: In function 'int main()':
port_facility.cpp:111:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  111 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~