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struct seg {
pt a, b;
int id;
bool operator<(const seg& o) const {
if (real(a) < real(o.a)) {
int s = ccw(a, b, o.a);
return (s > 0 || (s == 0 && imag(a) < imag(o.a)));
} else if (real(a) > real(o.a)) {
int s = ccw(o.a, o.b, a);
return (s < 0 || (s == 0 && imag(a) < imag(o.a)));
}
return imag(a) < imag(o.a);
}
};
struct event {
pt p;
int id, type;
bool operator<(const event& o) const {
if (real(p) != real(o.p)) return real(p) < real(o.p);
if (type != o.type) return type > o.type;
return imag(p) < imag(o.p);
}
};
bool lessPT(const pt& a, const pt& b) {
return real(a) != real(b) ? real(a) < real(b)
: imag(a) < imag(b);
}
bool intersect(const seg& a, const seg& b) {
return lineSegmentIntersection(a.a, a.b, b.a, b.b);
}
pair<int, int> intersect(vector<seg>& segs) {
vector<event> events;
for (seg& s : segs) {
if (lessPT(s.b, s.a)) swap(s.b, s.a);
events.push_back({s.a, s.id, 1});
events.push_back({s.b, s.id, -1});
}
sort(all(events));
set<seg> q;
vector<set<seg>::iterator> where(sz(segs));
for (auto e : events) {
int id = e.id;
if (e.type > 0) {
auto it = q.lower_bound(segs[id]);
if (it != q.end() && intersect(*it, segs[id]))
return {it->id, segs[id].id};
if (it != q.begin() && intersect(*prev(it), segs[id]))
return {prev(it)->id, segs[id].id};
where[id] = q.insert(it, segs[id]);
} else {
auto it = where[id];
if (it != q.begin() && next(it) != q.end() && intersect(*next(it), *prev(it)))
return {next(it)->id, prev(it)->id};
q.erase(it);
}
}
return {-1, -1};
}
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