String

  1. Should the input contain only alphanumeric characters, or can it include other characters as well?
  2. How should uppercase and lowercase characters be treated—should they be considered equivalent or distinct?

Array

  1. Is the input sorted?
  2. If the task involves sorting, should it be done in-place, or is extra space allowed?
  3. Is it permissible to modify the input array?
  4. Can the array contain duplicate values? If so, how should duplicate values be handled or treated?

Numbers

  1. Are the numbers expected to be integers only, and if so, should they be positive, negative, or whole numbers?
  2. Is there any input constraint? How big can a number be?