Script – 00-09 Jan 27

function sockMerchant(n, ar) {
  ar.sort(function (a, b) {
    return a - b;
  });

  let groups = [];
  for (let i = 0, j = 1; i < ar.length; i += 2, j += 2) {
    if (ar[i] === ar[j]) {
      groups.push(ar.slice(i, i + 2));
    } else {
      i - 1;
      j - 1;
    }
  }

  return groups.length;
}