title: Memory efficient way to store strings
body: <p>Assume I have millions strings. Each string has an int value. I want to retrieve this value by  input string but I don't want to store all this strings because they take a lot of space. I can't use hash table because of it need to store all or at least many strings in memory. So what is good data structure for my case (I don't need to add or delete any strings, I am already have prepared data and read is only allowed operation)</p>