const merge = (leftArr, rightArr, OG) => {
  const leftSize = leftArr.length;
  const rightSize = rightArr.length;
  const ogSize = OG.length;
  let lefty = 0;
  let righty = 0;
  let oggy = 0;
  while(lefty < leftSize && righty < rightSize) {
    if(leftArr[lefty] < rightArr[righty]) {
      OG[oggy] = leftArr[lefty];
      lefty++;
    } else {
      OG[oggy] = rightArr[righty];
      righty++;

    }
    oggy++;
  }
  while(lefty < leftSize) {
    OG[oggy] = leftArr[lefty];
    lefty++;
    oggy++;
  }
  while(righty < rightSize) {
    OG[oggy] = rightArr[righty];
    righty++;
    oggy++;
  }
  return OG;
}
const mergeSort = (arr) => {
  const size = arr.length;
  if(arr.length <= 1){
    return arr;
  }
  const midPoint = Math.round(size/2) - 1;
  const leftPart = arr.slice(0,midPoint+1);
  const rightPart = arr.slice(midPoint+1);
  mergeSort(leftPart);
  mergeSort(rightPart);
  merge(leftPart, rightPart, arr);
  return arr;
}