Point in Polygon

#include <iostream>
#include <vector>

using namespace std;

#define ll long long

int crossings(pair<ll, ll> point, const vector<pair<ll, ll>>& poli) {
    ll x = point.first;
    ll y = point.second;
    ll n = poli.size();
    ll crossings = 0;

    for (int i = 0; i < n; i++) {
        ll x1 = poli[i].first;
        ll y1 = poli[i].second;
        ll x2 = poli[(i + 1) % n].first;
        ll y2 = poli[(i + 1) % n].second;

        if ((y - y1) * (x2 - x1) == (x - x1) * (y2 - y1) &&
            min(x1, x2) <= x && x <= max(x1, x2) &&
            min(y1, y2) <= y && y <= max(y1, y2)) {
            return 2; 
        }

        if ((y1 <= y && y < y2) || (y2 <= y && y < y1)) {
            double x_intersect = x1 + (double)(y - y1) * (x2 - x1) / (y2 - y1);
            if (x < x_intersect)crossings++;
        }
    }
    if (crossings % 2 == 1) return 0;
    return 1;
}

int main() {
    int n, m;
    cin >> n >> m;

    vector<pair<ll, ll>> poli(n);

    for (int i = 0; i < n; i++) {
        ll a, b;
        cin >> a >> b;
        poli[i] = make_pair(a, b);
    }

    for (int i = 0; i < m; i++) {
        ll a, b;
        cin >> a >> b;
        int cross = crossings(make_pair(a, b), poli);
        if (cross == 0)
            cout << "INSIDE" << endl;
        else if (cross == 1)
            cout << "OUTSIDE" << endl;
        else
            cout << "BOUNDARY" << endl;
    }

    return 0;
}

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