Pascal Triangle

function pascals_triangle($n) {
  // Your code here
  $firstRow = [1];
  $secondRow = [1,1];
  $rows = [
    1 => $firstRow,
    2 => $secondRow
  ];

  // when n is 1 or 2, return rowOne or rowTwo
  if ($n == 1) {
    return $rows[1];
  }
  if ($n == 2) {
    return array_merge($firstRow, $secondRow);
  }

  for ($row = 3; $row <= $n; $row++) {
    $prev = $rows[$row-1];

    // start is always 1
    $currentRow = [1];

    for ($i = 1; $i < $row - 1; $i++) {
      // current num
      $currentNum = $prev[$i - 1] + $prev[$i];
      $currentRow[] = $currentNum;
    }

    // add the end
    $currentRow[] = 1;
    $rows[] = $currentRow;
  }

  $result = [];
  foreach ($rows as $row) {
    $result = array_merge($result, $row);
  }

  return $result;
}