1 files changed, 85 insertions, 0 deletions
diff --git a/17/day1/arboreal.cpp b/17/day1/arboreal.cpp
new file mode 100644
index 0000000..659216b
--- /dev/null
+++ b/17/day1/arboreal.cpp
@@ -0,0 +1,85 @@
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+#define f first
+#define s second
+using namespace std;
+using namespace __gnu_pbds;
+using ii = pair<int, int>;
+template<typename T> using ordered_set = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;
+constexpr int MAXN = 100001;
+
+vector<int> T[MAXN + 1];
+ordered_set<int> S[4 * MAXN + 4];
+
+void build(int l = 0, int r = MAXN, int n = 1) {
+	if (l == r) {
+		for (auto& y : T[l]) S[n].insert(y);
+	}
+	else {
+		int m = (l + r) >> 1;
+		build(l, m, n << 1), build(m + 1, r, n << 1 | 1);
+		for (auto& y : S[n << 1]) S[n].insert(y);
+		for (auto& y : S[n << 1 | 1]) S[n].insert(y);
+	}
+}
+
+int query(int xl, int xr, int yl, int yr, int l = 0, int r = MAXN, int n = 1) {
+	if (l > r || l > xr || r < xl) return 0;
+	if (l >= xl && r <= xr) return S[n].order_of_key(yr + 1) - S[n].order_of_key(yl);
+	else {
+		int m = (l + r) >> 1;
+		return query(xl, xr, yl, yr, l, m, n << 1) + query(xl, xr, yl, yr, m + 1, r, n << 1 | 1);
+	}
+}
+ 
+ii P[100001];
+ 
+int main() {
+	ios_base::sync_with_stdio(0), cin.tie(0);
+
+	int N; cin >> N;
+	for (int i = 0; i < N; ++i) cin >> P[i].f >> P[i].s;
+ 
+	vector<ii> tmp;
+	for (int i = 0; i < N; ++i) tmp.emplace_back(P[i].f, i);
+	sort(begin(tmp), end(tmp));
+	for (int i = 0; i < N; ++i) {
+		if (i && tmp[i].f == tmp[i - 1].f) P[tmp[i].s].f = P[tmp[i - 1].s].f;
+		else P[tmp[i].s].f = i;
+	}
+	tmp.clear();
+	for (int i = 0; i < N; ++i) tmp.emplace_back(P[i].s, i);
+	sort(begin(tmp), end(tmp));
+	for (int i = 0; i < N; ++i) {
+		if (i && tmp[i].f == tmp[i - 1].f) P[tmp[i].s].s = P[tmp[i - 1].s].s;
+		else P[tmp[i].s].s = i;
+	}
+	
+	for (int i = 0; i < N; ++i) T[P[i].f].push_back(P[i].s);
+	build();
+	
+	vector<ii> X, Y;
+	for (int i = 0; i < N; ++i) X.push_back(P[i]), Y.push_back(P[i]);
+ 
+	auto cmpy = [](const ii & a, const ii & b) { return a.s < b.s || (a.s == b.s && a.f < b.f); };
+	sort(begin(X), end(X));
+	sort(begin(Y), end(Y), cmpy);
+	unique(begin(X), end(X));
+	unique(begin(Y), end(Y), cmpy);
+ 
+	int ans = 0;
+	for (int i = 0; i < N; ++i) {
+		auto it = lower_bound(begin(X), end(X), ii(P[i].f, P[i].s));
+		int yh = (next(it) != end(X) && next(it)->f == P[i].f ? next(it)->s : MAXN + 1);
+		int yl = (it != begin(X) && prev(it)->f == P[i].f ? prev(it)->s : -2);
+ 
+		it = lower_bound(begin(Y), end(Y), ii(P[i].f, P[i].s), cmpy);
+		int xh = (next(it) != end(Y) && next(it)->s == P[i].s ? next(it)->f : MAXN + 1);
+		int xl = (it != begin(Y) && prev(it)->s == P[i].s ? prev(it)->f : -2);
+ 
+		int q = query(xl + 1, xh - 1, yl + 1, yh - 1);
+		if (q > 1) ++ans;
+	}
+	cout << ans << '\n';
+}