题解 | 直线与圆交点间距

import math

class Point:
    def __init__(self, A, B):
        self.x = A
        self.y = B

class Line:
    def __init__(self, A, B):
        self.point_A = A
        self.point_B = B
        self.kA = B.y - A.y
        self.kB = A.x - B.x
        self.kC = B.x * A.y - A.x * B.y


class Circle:
    def __init__(self, A, B):
        self.O = A
        self.r = B
    
def get_distance(P, l):
    # TODO: 计算点P到直线l的距离
    if l.point_A.x == l.point_B.x:  
        return abs(P.x - l.point_A.x)
    else:
        return abs(l.kA * P.x + l.kB * P.y + l.kC)/(math.sqrt(l.kA ** 2 + l.kB ** 2))

def getDistance(circle, l):
    # 请在这里实现你的代码
    if l.point_A.x == l.point_B.x and l.point_A.y == l.point_B.y:
        return circle.r
    else:
        distance = get_distance(circle.O, l)
        if distance >= circle.r:
            return 0.0
        else:
            return math.sqrt(circle.r ** 2 - distance ** 2) * 2
    pass














































































































































































































def main():
    ox, oy, r = map(float, input().split())
    x1, y1, x2, y2 = map(float, input().split())
    
    center = Point(ox, oy)
    circle = Circle(center, int(r))
    
    p1 = Point(x1, y1)
    p2 = Point(x2, y2)
    l = Line(p1, p2)
    
    result = getDistance(circle, l)
    print("{:.6f}".format(result))

if __name__ == "__main__":
    main()