How to perform a binary search of a text file

Since the content of the file does not change, you can break the file into multiple pieces. Say A-G, H-N, 0-T and U-Z. This allows you to check the first character and immediately be able to cut the possible set to a fourth of the original size. Now a linear search will not take as long or reading the whole file could be an option. This process could be extended if n/4 is still too large, but the idea is the same. Build the search breakdowns into the file structure instead of trying to do it all in memory.