478. Generate Random Point in a Circle (Medium)
https://leetcode.com/problems/generate-random-point-in-a-circle/
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:
- input and output values are in floating-point.
- radius and x-y position of the center of the circle is passed into the class constructor.
- a point on the circumference of the circle is considered to be in the circle.
randPointreturns 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.
Solutions
class Solution {
double r;
double x;
double y;
public Solution(double radius, double x_center, double y_center) {
r = radius;
x = x_center;
y = y_center;
}
public double[] randPoint() {
double rx = 0;
double ry = 0;
int maxInt = (1 << 31) - 1;
Random rand = new Random();
do {
// The special case of below statements is that the circle center is never covered.
// The reason is that Math.random returns a value range in [0, 1), 0 inclusive 1 exclusive.
// rx = x + (1 - Math.random()) * r;
// ry = y + (1 - Math.random()) * r'
// The nextInt() method of Random accepts a bound integer and returns a random integer
// from 0 (inclusive) to the specified bound (exclusive). By default, the specified bound
// is (1<<31)-1
// To make rand.nextInt() produce values in [0,1], both 0 and 1 are inclusive, use
// following lines. Don't forget to deduct 1 from maxInt since the maximum rand.nextInt()
// can reach is maxInt-1.
rx = x + rand.nextInt() * 1.0 / (maxInt - 1) * r;
ry = y + rand.nextInt() * 1.0 / (maxInt - 1) * r;
} while (Math.pow(rx - x, 2) + Math.pow(ry - y, 2) > Math.pow(r, 2));
// Points out of the boundary of the circle are rejected.
return new double[]{rx, ry};
}
}