Design CombinationIterator classcombinationiteratorstre character int combinationlength Initializes object string character sort distinct lowercase english letter number combinationlength argumentsnext return combination length combinationlength lexicographical orderhasNext return true exist combination Example 1inputcombinationiterator hasnext hasnext hasNextabc 2 Outputnull ab true ac true bc falseexplanationcombinationiterator itr new CombinationIteratorabc 2itrnext return abitrhasNext return Trueitrnext return acitrhasnext return Trueitrnext return bcitrhasnext return false Constraints1 combinationlength characterslength 15all character character uniqueAt 104 call hasNextIt guarantee call function valid