When an ArrayList in Java reaches its full capacity, the strategy for increasing this capacity is not explicitly defined. Consider the following strategies of increasing the ArrayList's capacity, which one ensures an amortized $(1)$ running time for the add operation?

Question $1$ options:

Increase the capacity by a random number each time the array is full.

Increase the capacity by $10$ each time the array is full.

Double the capacity each time the array is full.

Increase the capacity by $1$ each time the array is full.