Question

This is for an assignment, and is in psuedo-code.

I need to find how many integers in an array are unique, nothing else, but it has to be in O(n), preferably without hashing.

Thanks!

Answer 1

What about this pseudo code?

array randomNumbers;
array unique;
int uniqueCount = 0;

for (i in randomNumbers) {

  unique[i] += 1;
  uniqueCount++; //count all here
  // and remove duplicities here
  if (unique[i] > 1) {
    uniqueCount--;
  }
}
return uniqueCount;

And the premis is, that undeclared unique[i] is 0