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`.