CustomerActivity.java

public class CustomerActivity {

    private final int[] months = new int[12];

    public void record(LocalDate day) {
        int monthOffSet = day.getMonthValue() - 1;
        int monthValue = months[monthOffSet];
        // Set bit for day in 32 bit int and then OR(|) with month value to merge value
        months[monthOffSet] = monthValue | 1 << (day.getDayOfMonth() - 1);
    }

    public int daysActive(Month month) {
        int monthValue = months[month.ordinal()];
        return countBits(monthValue);
    }

    public boolean wasActive(LocalDate day) {
        int monthOffSet = day.getMonthValue() - 1;
        int monthValue = months[monthOffSet];
       // Set bit for day in 32 bit int and then AND(|) with month value to check if bit was set
        return (monthValue & 1 << (day.getDayOfMonth() - 1)) > 0;
    }
   
}