Singleton

Singleton is a most widely used design pattern. If a class has and only has one instance at every moment, we call this design as singleton. For example, for class Mouse (not a animal mouse), we should design it in singleton.

You job is to implement a getInstance method for given class, return the same instance of this class every time you call this method.

Example

In Java:

A a = A.getInstance();
A b = A.getInstance();

a should equal to b.

class Solution {
    /**
     * @return: The same instance of this class every time
     */
    private static Solution instance;

    private Solution(){
    }
    public static synchronized Solution getInstance() {
        // write your code here
        if (instance == null){
            instance = new Solution();
            return instance;
        } else {
            return instance;
        }
    }
};