Day6 Pull Request for Code Review

Please refactor these to (1) avoid magic numbers, (2) improve logic, (3) shorten the codes :bow: 
Example:
```
int totalCount = 0;

if (choices==EASY) {
    totalCount = 5;
} else if (choices = MEDIUM) {
    totalCount = 20;
} else {
    totalCount = 40;
}

for (int i = o; i < totalCount; i++) {
    arrayList.add(i);
}```