0, 'A' => 1, 'B' => 2, 'C' => 3, 'D' => 4, 'E' => 5, 'F' => 6, 'G' => 7, 'H' => 8, 'I' => 9, 'J' => 10, 'K' => 11, 'L' => 12, 'M' => 13, 'N' => 14, 'O' => 15, 'P' => 16, 'Q' => 17, 'R' => 18, 'S' => 19, 'T' => 20, 'U' => 21, 'V' => 22, 'W' => 23, 'X' => 24, 'Y' => 25, ]; $answer = ''; for($i = 0; $i < count($s); $i++){ $char = $s[$i]; $char_num = $alphabet[$char]; if($i + 1 > 25){ $char_num = $char_num - (($i + 1) % 26); } else { $char_num = $char_num - ($i + 1); } foreach($alphabet as $key => $value){ if($char_num === $value){ $answer .= $key; } } } echo $answer;