title: What is the most efficient way to tell if a string of unicode characters has unique characters in C++?
body: <p>If it was just ASCII characters I just use array of bool of size 256. But Unicode has so many characters. 
   1. Wikipedia says unicode has more than 110000 characters. So bool[110000] might not be a good idea?
   2. Lets say the characters are coming in a stream and I just want to stop whenever a duplicate is detected. How do I do this?
   3. Since the set is so big, I was thinking hash table. But how do I tell when the collision happens because I do not want to continue once a collision is detected. Is there a way to do this in STL implementation of hash table? </p>
  
  <p>Efficient in terms of speed and memory utilization. </p>