function minimumDistances(a) {
  const len = a.length;
  let stack = [];

  for (let i = 0; i < len; i++) {
    const f = a[i];
    const s = a.indexOf(f, i + 1);
    if (s !== -1) {
      stack.push(Math.abs(i - s));
    }
  }

  return stack.length ? Math.min(...stack) : -1;
}