用PHP迭代器來實現一個斐波納契數列

斐波納契數列通常做法是用遞歸實現，當然還有其它的方法。這里現學現賣，用PHP的迭代器來實現一個斐波納契數列，幾乎沒有什么難度，只是把類里的next()方法重寫了一次。注釋已經寫到代碼中，也是相當好理解的。

    <?php

    / 
    @author nicesunboy@gmail.com 
    */

    class Fibonacci implements Iterator {

        private $previous = 1;

        private $current = 0;

        private $key = 0;


    public function current() {   
        return $this->current;   
    }   

    public function key() {   
        return $this->key;   
    }   

    public function next() {   
        // 關鍵在這里  
        // 將當前值保存到  $newprevious  
        $newprevious = $this->current;   
        // 將上一個值與當前值的和賦給當前值  
        $this->current += $this->previous;   
        // 前一個當前值賦給上一個值  
        $this->previous = $newprevious;   
        $this->key++;   
    }   

    public function rewind() {   
        $this->previous = 1;   
        $this->current = 0;   
        $this->key = 0;   
    }   

    public function valid() {   
        return true;   
    }   
}   

$seq = new Fibonacci;   
$i = 0;   
foreach ($seq as $f) {   
    echo "$f ";   
    if ($i++ === 15) break;   
}   
?>  </pre> 


  程序運行結果：
    0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610