I need to code and implement optimal prefix free coding scheme to encode a text

Question

I need to code and implement optimal prefix free coding scheme to encode a text file into a DNA string (a string of characters from the alphabet {A,C,G,T}). the algorithm should take as input a text file and create 2 output files:

1) The first output file should list each ASCII character from the input file along with its corresponding DNA encoding.

2) The second output file should contain a single sequence of DNA bases representing the input file encoded into a single DNA string.



I have trouble understanding what it wants as explained below

Phase 1: Read in the input file and count the number of occurrences of each character in the file.

Phase 2: Using the character frequencies from phase 1, generate the optimal four character prefix free encoding for the input file. Create the 2 output files as specified.



Phase 1 should run in time linear in the size of the file, O(filesize). Phase 2 should run in time (n log n) where n is the number of distinct characters encountered in the file.

if you could please help me that would be much appreciated!

Explanation / Answer

check these links..... http://biopython.org/DIST/docs/tutorial/Tutorial.html http://web.virginia.edu/Heidi/chapter11/chp11frameset.htm http://www.answers.com/topic/gene

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