Polygon area

#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

struct Point {
    long long x, y;
};

long long polygonArea(const vector<Point>& vertices) {
    int n = vertices.size();
    long long area = 0;

    for (int i = 0; i < n; i++) {
        int j = (i + 1) % n; 
        area += vertices[i].x * vertices[j].y - vertices[i].y * vertices[j].x;
    }

    return abs(area);
}

int main() {
    int n;
    cin >> n;
    vector<Point> vertices(n);

    for (int i = 0; i < n; i++) {
        cin >> vertices[i].x >> vertices[i].y;
    }

    cout << polygonArea(vertices) << endl;

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED