Template/Geometry.cpp at master · return-100/Template · GitHub

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/*** Point Structure ***/

class point
{
public:
    int x, y;

    /*** Use for Polar Sort ***/

    bool operator < (point b)
    {
        if (y != b.y)
            return y < b.y;

        return x < b.x;
    }

    /*** Use for Montone Chain ***/

    bool operator < (point b)
    {
        return (x < b.x || (x == b.x && y < b.y));
    }
};


double dist(point a, point b)
{
    return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

long long area(point a, point b, point c)
{
    return (a.x - b.x) * (b.y - c.y) - (a.y - b.y) * (b.x - c.x);
}

/*** -1 = anti - clockwise, 0 = co - linear, 1 = clockwise ***/

int clockwiseCheck(point a, point b, point c)
{
    int area = (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);

    if (area > 0)
        return -1;
    else if (area < 0)
        return 1;
    return 0;
}

/*** Used in Graham Scan to Sort the Point according to their Polar Angle ***/

bool polarOrder(point a, point b)
{
    int order = clockwiseCheck(pivot, a, b);

    if (order == 0)
        return dist(pivot, a) < dist(pivot, b);

    return (order == -1);
}

/*** Montone Chain Method for finding Convex Hull ***/

void convexHull()
{
    sort(arr, arr + n);

    for (int i = 0; i < n; ++i)
    {
        while (idx > 1 && area(cvx[idx - 2], cvx[idx - 1], arr[i]) <= 0)
            --idx;

        cvx[idx++] = arr[i];
    }

    int var = idx;

    for (int i = n - 2; i >= 0; --i)
    {
        while (idx > var && area(cvx[idx - 2], cvx[idx - 1], arr[i]) <= 0)
            --idx;

        cvx[idx++] = arr[i];
    }
}