Finished c and d, e doesn't check for faulty arrangements

atcoder/beginner_contests/226/d.cpp

@@ -2,23 +2,57 @@
 
 using namespace std;
 
-void test_case(int tc){
+typedef long long ll;
 
+set<pair<ll, ll>> spells;
+
+ll gcd(ll a, ll b){
+    if(b == 0){
+        return a;
+    }
+
+    return gcd(b, a % b);
 }
 
-
-
 int main(){
     ios::sync_with_stdio(0);
     cin.tie(0);
 
-    int t;
-    cin >> t;
+    int n;
+    cin >> n;
 
-    for(int tc = 1; tc <= t; ++tc){
-        test_case(tc);
+    vector<pair<ll, ll>> cities(n);
+
+    for(int i = 0; i < n; ++i){
+        ll x, y;
+
+        cin >> x >> y;
+        cities[i] = {x, y};
+
+        for(int j = 0; j < i; ++j){
+            ll dx = cities[j].first - cities[i].first;
+            ll dy = cities[j].second - cities[i].second;
+
+            if(dx == 0){
+                spells.insert({0, 1});
+                spells.insert({0,-1});
+            } else if(dy == 0){
+                spells.insert({1,0});
+                spells.insert({-1, 0});
+            } else{
+                ll g = gcd(dx, dy);
+
+                dx /= g;
+                dy /= g;
+
+                spells.insert({dx, dy});
+                spells.insert({-1*dx, -1*dy});
+            }
+        }
     }
 
+    cout << spells.size();
+
     cout << flush;
 
     return 0;