[Swift]LeetCode478. 在圆内随机生成点 | Generate Random Point in a Circle

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Given the radius and x-y positions of the center of a circle, write a function randPoint which generates a uniform random point in the circle.

Note:

1. input and output values are in floating-point.
2. radius and x-y position of the center of the circle is passed into the class constructor.
3. a point on the circumference of the circle is considered to be in the circle.
4. randPoint returns a size 2 array containing x-position and y-position of the random point, in that order.

Example 1:

Input: 
["Solution","randPoint","randPoint","randPoint"]
[[1,0,0],[],[],[]]
Output: [null,[-0.72939,-0.65505],[-0.78502,-0.28626],[-0.83119,-0.19803]]

Example 2:

Input: 
["Solution","randPoint","randPoint","randPoint"]
[[10,5,-7.5],[],[],[]]
Output: [null,[11.52438,-8.33273],[2.46992,-16.21705],[11.13430,-12.42337]]

Explanation of Input Syntax:

The input is two lists: the subroutines called and their arguments. Solution's constructor has three arguments, the radius, x-position of the center, and y-position of the center of the circle. randPoint has no arguments. Arguments are always wrapped with a list, even if there aren't any.

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给定圆的半径和圆心的 x、y 坐标，写一个在圆中产生均匀随机点的函数 randPoint 。

说明:

1. 输入值和输出值都将是浮点数。
2. 圆的半径和圆心的 x、y 坐标将作为参数传递给类的构造函数。
3. 圆周上的点也认为是在圆中。
4. randPoint 返回一个包含随机点的x坐标和y坐标的大小为2的数组。

示例 1：

输入: 
["Solution","randPoint","randPoint","randPoint"]
[[1,0,0],[],[],[]]
输出: [null,[-0.72939,-0.65505],[-0.78502,-0.28626],[-0.83119,-0.19803]]

示例 2：

输入: 
["Solution","randPoint","randPoint","randPoint"]
[[10,5,-7.5],[],[],[]]
输出: [null,[11.52438,-8.33273],[2.46992,-16.21705],[11.13430,-12.42337]]

输入语法说明：

输入是两个列表：调用成员函数名和调用的参数。Solution 的构造函数有三个参数，圆的半径、圆心的 x 坐标、圆心的 y 坐标。randPoint 没有参数。输入参数是一个列表，即使参数为空，也会输入一个 [] 空列表。

---

拒绝采样的经典应用: [Swift]LeetCode470. 用 Rand7() 实现 Rand10() | Implement Rand10() Using Rand7()

Runtime: 736 ms

Memory Usage: 17.5 MB

class Solution {
    var r:Double
    var centerX:Double
    var centerY:Double

    init(_ radius: Double, _ x_center: Double, _ y_center: Double) {
        self.r = radius
        self.centerX = x_center
        self.centerY = y_center        
    }
    
    func randPoint() -> [Double] {
        while(true)
        {
            var x:Double = (2 * Double.random(in: 0..<1) - 1.0) * r
            var y:Double = (2 * Double.random(in: 0..<1) - 1.0) * r

            if x * x + y * y <= r * r
            {
                return [centerX + x, centerY + y]
            }
        }
    }
}

/**
 * Your Solution object will be instantiated and called as such:
 * let obj = Solution(radius, x_center, y_center)
 * let ret_1: [Double] = obj.randPoint()
 */
 

---

Runtime: 748 ms

Memory Usage: 17.5 MB

class Solution {
    var r:Double
    var centerX:Double
    var centerY:Double

    init(_ radius: Double, _ x_center: Double, _ y_center: Double) {
        self.r = radius
        self.centerX = x_center
        self.centerY = y_center        
    }
    
    func randPoint() -> [Double] {
        var theta:Double = 2 * M_PI * (Double.random(in: 0..<1))
        var len:Double = sqrt(Double.random(in: 0..<1)) * r
        return [centerX + len * cos(theta), centerY + len * sin(theta)]      
    }
}

/**
 * Your Solution object will be instantiated and called as such:
 * let obj = Solution(radius, x_center, y_center)
 * let ret_1: [Double] = obj.randPoint()
 */