header(‘Content-Type:text/html; charset=utf-8‘);
echo ‘Convert number to title of excel.<br>‘;

function showarr($arr){
    echo ‘<pre>‘;
    print_r($arr);
    echo ‘</pre><br>‘;
}

$ea = new ExcelAssistant();
$test1 = $ea->GetExcelTit(27);
showarr($test1);

/**
 * Excel助手
 * @author RexCao 2015-01-08
 */
class ExcelAssistant{
    private $carr = array();//结果数组，初始值为A
    private $curlet = ‘A‘;//当前末尾字母，初始化为A
    private $curletpi = 0;//当前字符串从右向左的位数，用来上位递归加1处理（从0开始）
    private $tmpar = array(‘A‘);//临时数组，存储结果字符串上每位的字符。初始值为‘A‘
    private static $a = array(‘A‘,‘B‘,‘C‘,‘D‘,‘E‘,‘F‘,‘G‘,‘H‘,‘I‘,‘J‘,‘K‘,‘L‘,‘M‘,‘N‘,‘O‘,‘P‘,‘Q‘,‘R‘,‘S‘,‘T‘,‘U‘,‘V‘,‘W‘,‘X‘,‘Y‘,‘Z‘);
    private static $b = array(‘A‘=>0,‘B‘=>1,‘C‘=>2,‘D‘=>3,‘E‘=>4,‘F‘=>5,‘G‘=>6,‘H‘=>7,‘I‘=>8,‘J‘=>9,‘K‘=>10,‘L‘=>11,‘M‘=>12,‘N‘=>13,‘O‘=>14,‘P‘=>15,‘Q‘=>16,‘R‘=>17,‘S‘=>18,‘T‘=>19,‘U‘=>20,‘V‘=>21,‘W‘=>22,‘X‘=>23,‘Y‘=>24,‘Z‘=>25);
    
    /**
     * 获取excel列头
     * @param $num 列数总计
     */
    public function GetExcelTit($num){
        $i = 0;
        while($i<$num){
            $this->curletpi = 0;//没有处理上位的时候，只处理当前位
            $this->tmpar[count($this->tmpar)-1] = $this->curlet;
            $this->carr[] = implode(‘‘,$this->tmpar);
            $this->curlet = $this->GetNextLetter($this->curlet);
            
            if($this->curlet == ‘A‘){
                //说明过了一圈，该向上位递归加1了
                $this->curletpi++;//从当前位左边的那位开始处理
                $this->RecursiveAddUp();
            }
            $i++;
        }
        return $this->carr;
    }

    /**
     * 根据字母获取下位字母
     * A-Z循环
     */
    public function GetNextLetter($l){
        $k = self::$b[$l];//当前字母索引
        $k++;//下位字母索引
        if($k == 26){
            $l = ‘A‘;//反转
        }else{
            $l = self::$a[$k];
        }
        return $l;
    }

    /**
     * 递归向上位加一
     * 在这里，只有一次计算结果为A后，才会向上加1，
     * 但不是每个位加了之后都要往上位冒泡，所以不能遍历每个位
     * @author RexCao
     */
    public function RecursiveAddUp(){
        //先更新最右位的字母
        $this->tmpar[count($this->tmpar)-1] = ‘A‘;
        if($this->curletpi+1>count($this->tmpar)){
            $this->tmpar = array_merge(array(‘A‘),$this->tmpar);
        }else{
            $cl = $this->tmpar[count($this->tmpar)-$this->curletpi-1];//当前位的字母
            $cl = $this->GetNextLetter($cl);
            if($cl == ‘A‘){
                $this->tmpar[count($this->tmpar)-$this->curletpi-1] = ‘A‘;//要去处理更上位了，先更新本位
                $this->curletpi++;//再上一位
                $this->RecursiveAddUp();
            }else{
                //更新当前位的字母为新字母即可
                $this->tmpar[count($this->tmpar)-$this->curletpi-1] = $cl;
            }
        }
    }
}