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Polygon Area 384fe2b4

Polygon area via the shoelace formula. Works for any simple polygon (convex or not), vertices in either winding order.

Time: O(n). tested

content/geometry/polygon-area.h

ld polygonArea(vector<Point> &poly) {
    ld res = 0;
    int n = (int)poly.size();
    for (int i = 0; i < n; i++) res += poly[i].cross(poly[(i + 1) % n]);
    return abs(res) / 2.0;
}