nums with integers from 0 to combinationLength - 1.getNextCombination that updates nums to the next combination.getNextCombination, find the rightmost index j where nums[j] can be incremented.nums[j] and adjust the subsequent indices to form the next lexicographical combination.next(), convert the indices in nums to the corresponding string and call getNextCombination.hasNext(), return whether the current combination is not the last one.