LeetCode-in-Java

478. Generate Random Point in a Circle

Medium

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

import java.util.Random;

@SuppressWarnings("java:S2245")
public class Solution {
    private final double radius;
    private final double xCenter;
    private final double yCenter;
    private final Random random = new Random();

    public Solution(double radius, double xCenter, double yCenter) {
        this.radius = radius;
        this.xCenter = xCenter;
        this.yCenter = yCenter;
    }

    public double[] randPoint() {
        double x = getCoordinate(xCenter);
        double y = getCoordinate(yCenter);
        while (getDistance(x, y) >= radius * radius) {
            x = getCoordinate(xCenter);
            y = getCoordinate(yCenter);
        }
        return new double[] {x, y};
    }

    private double getDistance(double x, double y) {
        return (xCenter - x) * (xCenter - x) + (yCenter - y) * (yCenter - y);
    }

    private double getCoordinate(double center) {
        return center - radius + random.nextDouble() * 2 * radius;
    }
}

/*
 * Your Solution object will be instantiated and called as such:
 * Solution obj = new Solution(radius, x_center, y_center);
 * double[] param_1 = obj.randPoint();
 */

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