I try to use a hashset to solve this problem, but it always time exceed. I think my solution's time complexity is O(1). Can anyone give me some advice? Or tell me why this happened? orz

```
public class PhoneDirectory {
Set<Integer> set;
int max;
int min;
/** Initialize your data structure here
@param maxNumbers - The maximum numbers that can be stored in the phone directory. */
public PhoneDirectory(int maxNumbers) {
set = new HashSet<Integer>();
for(int i = 0; i < maxNumbers; i++) set.add(i);
max = maxNumbers - 1;
min = 0;
}
/** Provide a number which is not assigned to anyone.
@return - Return an available number. Return -1 if none is available. */
public int get() {
if(set.isEmpty()) return -1;
int res = set.iterator().next();
set.remove(res);
return res;
}
/** Check if a number is available or not. */
public boolean check(int number) {
if(number >= min && number <= max)
return set.contains(number);
else return false;
}
/** Recycle or release a number. */
public void release(int number) {
if(number > max || number < min) return;
set.add(number);
return;
}
}
```