--description--

Given a string representing a DNA sequence, return its complementary strand using the following rules:

• DNA consists of the letters "A", "C", "G", and "T".
• The letters "A" and "T" complement each other.
• The letters "C" and "G" complement each other.

For example, given "ACGT", return "TGCA".

--hints--

complementaryDNA("ACGT") should return "TGCA".

assert.equal(complementaryDNA("ACGT"), "TGCA");

complementaryDNA("ATGCGTACGTTAGC") should return "TACGCATGCAATCG".

assert.equal(complementaryDNA("ATGCGTACGTTAGC"), "TACGCATGCAATCG");

complementaryDNA("GGCTTACGATCGAAG") should return "CCGAATGCTAGCTTC".

assert.equal(complementaryDNA("GGCTTACGATCGAAG"), "CCGAATGCTAGCTTC");

complementaryDNA("GATCTAGCTAGGCTAGCTAG") should return "CTAGATCGATCCGATCGATC".

assert.equal(complementaryDNA("GATCTAGCTAGGCTAGCTAG"), "CTAGATCGATCCGATCGATC");

--seed--

--seed-contents--

function complementaryDNA(strand) {

  return strand;
}

--solutions--

function complementaryDNA(strand) {
  const complements = { A: "T", T: "A", C: "G", G: "C" };
  return strand
    .split("")
    .map(c => complements[c])
    .join("");
}