// assume start < end
// assume s <= start < end <= e
// return true if one or more than one item in [start, end) has been inserted
bool conflict(int start, int end) {
if (inserted) return true;
if (start == s && end == e) {
if (l == nullptr && r == nullptr) return inserted;
}
if (end <= p) {
return l == nullptr ? false : l->conflict(start, end);
}
else if (start < p && end > p) {
return (l == nullptr ? false : l->conflict(start, p)) ||
(r == nullptr ? false : r->conflict(p, end));
}
else // (start >= p) {
return r == nullptr ? false : r->conflict(start, end);
}
bool book(int start, int end) {
if (r.conflict(start, end))
return false;
r.insert(start, end);
return true;
}