complementaryDNA.js

// 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]


// Solution 

function DNAStrand(dna) {
  //your code here
  let str = '';
  for (let i = 0; i < dna.length; i++) {
    if (dna.charAt(i) == 'A') {
      str += 'T';
    }
    if (dna.charAt(i) == 'T') {

      str += 'A'
    }
    if (dna.charAt(i) == 'C') {

      str += 'G'
    }
    if (dna.charAt(i) == 'G') {

      str += 'C'
    }
  }
  return str;

}