题解 | 直线与圆交点间距

import java.util.Scanner;

class Point {
    double x, y;
    Point(double A, double B) {
        x = A;
        y = B;
    }
}

class Line {
    Point point_A, point_B;
    Line(Point A, Point B) {
        point_A = A;
        point_B = B;
    }
}

class Circle {
    Point O;
    int r;
    Circle(Point A, int B) {
        O = A;
        r = B;
    }
}

public class Main {
    public static double getDistance(Circle circle, Line l) {
        double A = l.point_B.y - l.point_A.y;
        double B = l.point_A.x - l.point_B.x;
        double C = -B * l.point_A.y + l.point_A.x * (-A);
        double temp = Math.pow(A, 2) + Math.pow(B, 2);
        double lower = Math.pow(temp, 0.5);
        temp = A * circle.O.x + B * circle.O.y + C;
        double upper = Math.abs(temp);
        double d = upper/lower;
        double ab05 = circle.r*circle.r-d*d;
        return 2*Math.pow(ab05,0.5);
    }



















































































































































































    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        double ox = scanner.nextDouble();
        double oy = scanner.nextDouble();
        int r = scanner.nextInt();

        double x1 = scanner.nextDouble();
        double y1 = scanner.nextDouble();
        double x2 = scanner.nextDouble();
        double y2 = scanner.nextDouble();

        Point center = new Point(ox, oy);
        Circle circle = new Circle(center, r);

        Point p1 = new Point(x1, y1);
        Point p2 = new Point(x2, y2);
        Line l = new Line(p1, p2);

        double result = getDistance(circle, l);
        System.out.printf("%.6f\n", result);

        scanner.close();
    }
}