solved 2171

Author: atobaum

2000/2171/2171.cpp

@@ -0,0 +1,45 @@
+#include <unordered_set>
+#include <bits/stdc++.h>
+using namespace std;
+
+typedef long long ll;
+typedef pair<int, int> pii;
+#define mp(a, b) make_pair(a, b)
+#define X first
+#define Y second
+
+#define FOR(i, a, b) for (int i = a; i < b; i++)
+
+int N, ans=0;
+ll bias = 1000000000;
+vector<pii> pts;
+unordered_set<ll> s;
+
+ll toLL(ll x, ll y){
+  return (x+bias)*2*bias + y+bias;
+}
+
+int main() {
+  ios::sync_with_stdio(false); cin.tie(NULL);
+  cin>>N;
+  FOR(i, 0, N){
+    int x, y;
+    cin>>x>>y;
+    pts.push_back(mp(x, y));
+    s.insert(toLL(x, y));
+  }
+
+  sort(pts.begin(), pts.end());
+
+  FOR(i, 0, N) FOR(j, i+1, N){
+    pii a = pts[i], b = pts[j];
+    if(a.X >= b.X || a.Y >= b.Y) continue;
+    if(s.find(toLL(a.X, b.Y)) != s.end() && s.find(toLL(b.X, a.Y)) != s.end()){
+      ++ans;
+    }
+  }
+
+  cout<<ans;
+
+  return 0;
+}