let arrayLength = 0

/* to create MAX  array */

function heapRoot (input, i) {
  const left = 2 * i + 1
  const right = 2 * i + 2
  let max = i

  if (left < arrayLength && input[left] > input[max]) {
    max = left
  }

  if (right < arrayLength && input[right] > input[max]) {
    max = right
  }

  if (max !== i) {
    swap(input, i, max)
    heapRoot(input, max)
  }
}

function swap (input, indexA, indexB) {
  [input[indexA], input[indexB]] = [input[indexB], input[indexA]]
}

export function heapSort (input) {
  arrayLength = input.length

  for (let i = Math.floor(arrayLength / 2); i >= 0; i -= 1) {
    heapRoot(input, i)
  }

  for (let i = input.length - 1; i > 0; i--) {
    swap(input, 0, i)
    arrayLength--

    heapRoot(input, 0)
  }
  return input
}