Forest

input/code.cpp: In function 'int main()':
input/code.cpp:41:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < v.size(); i++) {
                    ^
input/code.cpp:42:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0; j < v.size(); j++) {
                     ^

#include <iostream>
#include <algorithm>
#include <vector>
#define ll long long
#define P pair<ll, ll>

using namespace std;

bool p[2001];

bool isBetween(P a, P b) {
	ll cross = (a.first * b.second) - (b.first * a.second);
	ll dotp = (a.first * b.first) + (a.second * b.second);
	
	/*if (a.first == -1 && a.second == 2 && b.first == -2 && b.second == 4) {
		cout << "cross: " << cross << endl;
		cout << "dotp: " << dotp << endl;
	}*/

	if (!(b.first*b.first + b.second * b.second < a.first * a.first + a.second * a.second)) {
		return false;
	}

    if (cross != 0) return false;
	
	return (dotp>=0);
}

int main() {

	vector<pair<ll, ll>> v;
	int n, ux, uy, x, y;

	cin >> n >> ux >> uy;

	for (int i = 0; i < n; i++) {
		cin >> x >> y;
		v.push_back(P(x - ux, y - uy));
	}
	//käydään läpi joka pisteelle, että onko joku toinen piste sen ja (0,0) välissä. jos on, merkitään p[i] = true
	for (int i = 0; i < v.size(); i++) {
		for (int j = 0; j < v.size(); j++) {
			if (v[i] == v[j]) continue;
			if (isBetween(v[i], v[j])) {
				p[i] = true;
				
				
				/*cout << v[i].first << " " << v[i].second;
				cout << " on samalla linjalla kuin ";
				cout << v[j].first << " " << v[j].second << endl;*/
				break;
			}
		}
	}
	
	ll count = 0;
	for (int i = 0; i < n; i++) {
		if (p[i]) count++;
	}


	cout << n-count << endl;

}

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