Intersecting Lines POJ - 1269

#include <cmath>
#include <cstdio>
using namespace std;
/*
判断直线是否相交或者共线，并求出交点
*/

const double ESP = 1e-10;
int dcmp(double x) {
    if (fabs(x) < ESP) {
        return 0;
    } else {
        return x < 0 ? -1 : 1;
    }
}
//点
struct Point {
    double x, y;
    Point(double x = 0, double y = 0) : x(x), y(y) {}
};

//向量
typedef Point Vector;

Vector operator+(Vector A, Vector B) {
    return Vector(A.x + B.x, A.y + B.y);
}

Vector operator-(Point A, Point B) {
    return Vector(A.x - B.x, A.y - B.y);
}

Vector operator*(Vector A, double k) {
    return Vector(A.x * k, A.y * k);
}

Vector operator/(Vector A, double k) {
    return Vector(A.x / k, A.y / k);
}

bool operator<(const Point &A, const Point &B) {
    return A.x < B.x || (A.x == B.x && A.y < B.y);
}

bool operator==(const Point &A, const Point &B) {
    return dcmp(A.x - B.x) == 0 && dcmp(A.y - B.y) == 0;
}

double Dot(Vector A, Vector B) {
    return A.x * B.x + A.y * B.y;
}

double Cross(Vector A, Vector B) {
    return A.x * B.y - A.y * B.x;
}

//一个点是否在直线上
bool OnLine(Point A, Point B, Point P) {
    return dcmp(Cross(A - P, B - P)) == 0;
}

//两直线平行
bool isLineParallel(Point A, Point B, Point C, Point D) {
    return dcmp(Cross(A - B, C - D)) == 0 && !OnLine(A, B, C);
}

//两直线共线
bool isLineCommon(Point A, Point B, Point C, Point D) {
    return dcmp(Cross(A - B, C - D)) == 0 && OnLine(A, B, C);
}

//两直线交点
Point GetLineIntersection(Point P, Vector v, Point Q, Vector w) {
    Vector u = P - Q;
    double t = Cross(w, u) / Cross(v, w);
    return P + v * t;
}

const int MAXN = 100 + 5;
Point points[MAXN];
int n;

void slove() {
    printf("INTERSECTING LINES OUTPUT\n");

    for (int i = 0; i < n - 1; i += 4) {
        if (isLineCommon(points[i], points[i + 1], points[i + 2], points[i + 3])) {
            printf("LINE\n");
        } else if (isLineParallel(points[i], points[i + 1], points[i + 2], points[i + 3])) {
            printf("NONE\n");
        } else {
            Point ans = GetLineIntersection(points[i], points[i + 1] - points[i], points[i + 2], points[i + 3] - points[i + 2]);
            printf("POINT %.2lf %.2lf\n", ans.x, ans.y);//g++有毒.2f可以过.2lf过不了，或者用c++
        }
    }
    printf("END OF OUTPUT\n");
}

int main() {
    scanf("%d", &n);
    n *= 4;
    for (int i = 0; i < n; i += 4) {
        scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &points[i].x, &points[i].y, &points[i + 1].x, &points[i + 1].y,
              &points[i + 2].x, &points[i + 2].y, &points[i + 3].x, &points[i + 3].y);
    }
    slove();
    return 0;
}