478. Generate Random Point in a Circle

Description

Given the radius and the position of the center of a circle, implement the function randPoint which generates a uniform random point inside the circle.

Implement the Solution class:

• Solution(double radius, double x_center, double y_center) initializes the object with the radius of the circle radius and the position of the center (x_center, y_center).
• randPoint() returns a random point inside the circle. A point on the circumference of the circle is considered to be in the circle. The answer is returned as an array [x, y].

 

Example 1:

Input
["Solution", "randPoint", "randPoint", "randPoint"]
[[1.0, 0.0, 0.0], [], [], []]
Output
[null, [-0.02493, -0.38077], [0.82314, 0.38945], [0.36572, 0.17248]]

Explanation
Solution solution = new Solution(1.0, 0.0, 0.0);
solution.randPoint(); // return [-0.02493, -0.38077]
solution.randPoint(); // return [0.82314, 0.38945]
solution.randPoint(); // return [0.36572, 0.17248]

 

Constraints:

• 0 < radius <= 108
• -107 <= x_center, y_center <= 107
• At most 3 * 104 calls will be made to randPoint.

Solution

generate-random-point-in-a-circle.py

import random

class Solution(object):

    def __init__(self, radius, x_center, y_center):
        """
        :type radius: float
        :type x_center: float
        :type y_center: float
        """
        self.x_min, self.x_max = x_center - radius, x_center + radius
        self.y_min, self.y_max = y_center - radius, y_center + radius
        self.radius = radius
        self.x_center = x_center
        self.y_center = y_center

    def randPoint(self):
        """
        :rtype: List[float]
        """
        while True:
            x, y = random.uniform(self.x_min, self.x_max), random.uniform(self.y_min, self.y_max)
            if (x - self.x_center)**2 + (y - self.y_center)**2 <= self.radius**2:
                return [x, y]