RNA: Counting DNA Nucleotides
An RNA string is a string formed from the alphabet containing ‘A’, ‘C’, ‘G’, and ‘U’.
Given a DNA string corresponding to a coding strand, its transcribed RNA string is formed by replacing all occurrences of ‘T’ in with ‘U’ in .
Given: A DNA string having length at most 1000 nt.
Return: The transcribed RNA string of .
f <- "rna.txt" cat(gsub("T", "U", readLines(f)))