Forest

#include<bits/stdc++.h>
using namespace std;
typedef pair<int, int> ii;
#define X first
#define Y second

int gcd(int a, int b) {
  if(a < b) swap(a, b);
  if(b == 0) return a;
  int t = a % b;
  if(t == 0) return b;
  return gcd(t, b);
}

int main() {
  int n;
  cin >> n;
  int xU, yU;
  cin >> xU >> yU;
  vector<ii> v;
  for(int i = 0; i < n; ++i) {
    ii p;
    cin >> p.X >> p.Y;
    p.X -= xU;
    p.Y -= yU;
    int d = gcd(abs(p.X), abs(p.Y));
    p.X /= d; p.Y /= d;
    v.push_back(p);
  }
  sort(v.begin(), v.end());
  cout << unique(v.begin(), v.end()) - v.begin() << "\n";
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED