# How can we compress DNA string efficiently

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Category：Languages

DNA strings can be of any length comprising any combination of the 5 alphabets (A, T, G, C, N).
What could be the efficient way of compressing DNA string of alphabet comprising 5 alphabets (A, T, G, C, N). Instead of considering 3 bits per alphabet, can we compress and retrieve efficiently using less number of bits? Can anybody suggest a pseudo code for efficient compression and retrieval?

you can if you willing to (a) have different bits size for each char and (b) you are always reading from the start and never from the middle. then, you can have a code something like:

• A - 00
• T - 01
• G - 10
• C - 110
• N - 111

Reading from left to right you can only split a stream of bits to chars in one way. You read 2 bits at a time and if they are "11" you need to read one more bit to know what char it is.

This is based on Huffman Coding Algorithm

Note:
I don't know much about DNA, but if the probability of the chars is not equal (meaning 20% each). you should assign the shortest codes to those with the higher probability.