题解 | 直线与圆交点间距

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

class Line:
    def __init__(self, A:Point, B:Point):
        self.point_A = A
        self.point_B = B

class Circle:
    def __init__(self, A:Point, B:float):
        self.O = A
        self.r = B

def calculate_distance(P:Point,L:Line):
    circle_x = P.x
    circle_y = P.y
    x1 = L.point_A.x
    y1 = L.point_A.y
    x2 = L.point_B.x
    y2 = L.point_B.y
    if x1 == x2:
        return abs(circle_x - x1)
    # mx + y + c =0
    m = (y1 - y2) / (x1 - x2)
    A = -m
    B = 1
    C = m*x1 - y1
    distance = abs(A*circle_x + B*circle_y + C) / math.sqrt(A**2 + B**2)
    return distance

def getDistance(circle:Circle, distance:float):
    # 请在这里实现你的代码
    d = math.sqrt(circle.r**2 - (distance)**2)*2
    return d

if __name__ == "__main__":
    n = 1
    circle_x = 0
    circle_y = 0
    circle_r = 0
    x1 = 0
    y1 = 0
    x2 = 0
    y2 = 0    
    for line in sys.stdin:
        a = line.split()
        if n == 1:
            circle_x = float(a[0])
            circle_y = float(a[1])
            circle_r = float(a[2])
            n += 1
            continue
        if n == 2:
            x1,y1,x2,y2 = float(a[0]),float(a[1]),float(a[2]),float(a[3])
    circle_p = Point(circle_x,circle_y)
    A = Point(x1,y1)
    B = Point(x2,y2)
    L = Line(A,B)
    circle = Circle(circle_p,circle_r)
    
    distance = calculate_distance(circle_p,L)
    if circle_r == 0:
        print(0)
    elif circle_r>0:
        if distance > circle_r:
            print(float(0))
        else:
            print(getDistance(circle,distance))