function convertArray(arr, N) {
  let result = [], swapIndex = -1;
  for (let i = 0; i < arr.length; i++) {
    swapIndex = arr[(N * (i%N)) + i/N];
    while (swapIndex < i) {
      swapIndex = arr[(N * (swapIndex%N)) + swapIndex/N];
    }
    swap(arr, swapIndex, i);
  }
  return result;
}