ComplementaryDNA.js

// Complementary DNA

// 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". You 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"
// dnaStrand []        `shouldBe` []
// dnaStrand [A,T,G,C] `shouldBe` [T,A,C,G]
// dnaStrand [G,T,A,T] `shouldBe` [C,A,T,A]
// dnaStrand [A,A,A,A] `shouldBe` [T,T,T,T]

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

console.log(DNAStrand("AAAA"))//"TTTT","String AAAA is")
console.log(DNAStrand("ATTGC"))//"TAACG","String ATTGC is")
console.log(DNAStrand("GTAT"))//"CATA","String GTAT is")