The Hardest Easy Problem in Bioinformatics
Based on my experience of teaching bioinformatics to new programmers, the question - “extract the coding sequence of a multi-exon gene from the human (or other large eukaryotic) genome and translate it to find the protein sequence.” - can be classified as the hardest easy problem. Experienced bioinformaticians can answer the question without blinking, but those in this game for the first time find it extremely challenging.
It you are in the later camp, please check here for both R/Bioconductor and Biopython solutions.