Element distinctness problem – It is a well studied problem in many different models of computation. The problem may be solved by sorting the list and then checking if there are any consecutive equal elements; it may also be solved in linear expected time by a randomized algorithm that inserts each item into a hash table and compares only those elements that are placed in the same hash table cell. Stack Overflow – For a small set of nos. in range 0 to n we can use the approach of using the array index to maintain the count of each element. This approach has been used in array problem set.