Find Unique Characters in a File

Question

I have a file with 450,000+ rows of entries. Each entry is about 7 characters in length. What I want to know is the unique characters of this file.

For instance, if my f

Answer 1

Algorithm: Slurp the file into memory.

Create an array of unsigned ints, initialized to zero.

Iterate though the in memory file, using each byte as a subscript into the array.
    increment that array element.

Discard the in memory file

Iterate the array of unsigned int
       if the count is not zero,
           display the character, and its corresponding count.