#include<bits/stdc++.h> using namespace std; // #define int long long #define ll long long #define FOR(i, l, r) for(int i=l; i<=r; i++) #define FOD(i, r, l) for(int i=r; i>=l; i--) #define pii pair<int, int> #define fi first #define se second const int MAXN=1e5+5; int n, m; struct poin{ int x, y; }a[MAXN]; map<pii, int> ax2; int hx[]={1, 0, -1, 0}, hy[]={0, 1, 0, -1}; int tt[MAXN][5]; vector<int> adj[MAXN]; set<int> s; multiset<pair<pii, int>> ss; int vis[MAXN]; void dfs(int u){ vis[u]=1; for(auto v:adj[u]){ if(s.find(ax2[{u, v}])==s.end()){ ss.insert({{a[u].x, a[u].y}, u}); ss.insert({{a[v].x, a[v].y}, v}); s.insert(ax2[{u, v}]); } if(vis[v]) continue; dfs(v); } } int vst[MAXN][5]; int chk[MAXN]; void tinh(){ while(1){ if(s.empty()) break; if(ss.empty()) break; int u=(*ss.begin()).se; while(1){ if(ss.empty()) break; u=(*ss.begin()).se; int ok=0; for(auto v:adj[u]){ if(s.find(ax2[{u, v}])!=s.end()){ ok=1; break; } } if(!ok){ ss.erase(ss.begin()); } else{ break; } } if(ss.empty()) break; int h=1; set<pii> hist; while(1){ // cout << u << ' '; int ok=1; FOR(ii, ((h-1)%4+4)%4, ((h-1)%4+4)%4+3){ int i=ii%4; int v=tt[u][i]; // cout << v << ' '; if(v && s.find(ax2[{u, v}])!=s.end()){ if(vst[u][i]){ ok=1; break; } vst[u][i]=1; hist.insert({u, v}); u=v; h=i; ok=0; break; } } // cout << '\n'; if(ok) break; } int ok=1; for(auto [u, v]:hist){ // cout << u << ' ' << v << '\n'; int id=ax2[{u, v}]; if(hist.find({v, u})==hist.end()){ chk[id]=1; } if(s.find(id)!=s.end()){ ss.erase(ss.find({{a[u].x, a[u].y}, u})); ss.erase(ss.find({{a[v].x, a[v].y}, v})); s.erase(s.find(id)); ok=0; } } if(ok) break; } } signed main(){ ios_base::sync_with_stdio(false); cin.tie(NULL); // freopen("test.txt", "r", stdin); // freopen("o1.out", "w", stdout); if(fopen(".inp", "r")){ freopen(".inp", "r", stdin); freopen(".out", "w", stdout); } cin >> n; FOR(i, 1, n){ int x, y; cin >> x >> y; a[i]={x, y}; } cin >> m; FOR(i, 1, m){ int u, v; cin >> u >> v; ax2[{u, v}]=i; ax2[{v, u}]=i; adj[u].push_back(v); adj[v].push_back(u); FOR(_, 0, 1){ FOR(j, 0, 3){ if((a[v].x-a[u].x)*hx[j]>0 || (a[v].y-a[u].y)*hy[j]>0){ tt[u][j]=v; break; } } swap(u, v); } } FOR(i, 1, n){ if(!vis[i]){ s.clear(); ss.clear(); dfs(i); tinh(); } } int ans=0; vector<int> res; FOR(i, 1, m){ if(!chk[i]){ ans++; res.push_back(i); } } cout << ans << '\n'; for(auto x:res){ cout << x << '\n'; } return 0; }

flood.cpp: In function 'int main()':
flood.cpp:116:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  116 |                 freopen(".inp", "r", stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~
flood.cpp:117:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  117 |                 freopen(".out", "w", stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~