complementary_dna.js

// Description:
// Deoxyribonucleic acid (DNA) is a chemical found in the nucleus of cells and carries the "instructions" for the development and functioning of living organisms.
// If you want to know more: http://en.wikipedia.org/wiki/DNA
// In DNA strings, symbols "A" and "T" are complements of each other, as "C" and "G". Your function receives one side of the DNA (string, except for Haskell); you need to return the other complementary side. DNA strand is never empty or there is no DNA at all (again, except for Haskell).
// More similar exercise are found here: http://rosalind.info/problems/list-view/ (source)
// Example: (input --> output)
// "ATTGC" --> "TAACG"
// "GTAT" --> "CATA"

// SOLUTION:

function dnaStrand(dna) {
    let str = ""
    for (let i = 0; i < dna.length; i++) {
        if (dna[i] === "A") {
            str += "T";
        } else if (dna[i] === "T") {
            str += "A";
        } else if (dna[i] === "C") {
            str += "G";
        } else if (dna[i] === "G") {
            str += "C";
        }
    }
    return str;
}