Question

I have an ArrayList of ArrayLists. I want to make sure that each of the constituent ArrayLists has the same number of items. Is there any way to do this in less than n! time?

Answer 1

Absolutely! Iterate over the ArrayLists one at a time. Store the size of the first ArrayList, then confirm that the sizes of all the other ArrayLists match the size of the first list. Total time required is O(n), where n is the number of lists.

For example:

public static boolean listsHaveSameSize(List<List<?>> allLists) {
    List<?> first = null;
    for (List<?> list: allLists) {
        if (first == null) {
             first = list;
        } else if (list.size() != first.size()) {
             return false;
        }
    }
    return true;
}

Hope this helps!