如何获取字符串中具有相同字符的最长序列的长度?

function getLength($str)
{
  if (''===$str) return 0;
  preg_match_all('!(.)\\1*!', $str, $m);
  return max(array_map('strlen', $m[0]));
}

function getLongestSequence($str)
{
   $sl = strlen($str);
   $longest = 0;
   for($i = 0; $i < $sl; )
   {
       $substr = substr($str, $i);
       $len = strspn($substr, $substr{0});
       if($len > $longest)
           $longest = $len;
       $i += $len;
   }

   return $longest;
}

这是我的看法,它应该比regex和 substr 提供的解决方案:

function getLongestSequenceLength($string)
{
    $longest = $i = 0;
    $totalLength = strlen($string);
    while($i < $totalLength) {
        if(($length = strspn($string,  $string[$i], $i)) > $longest) {
            $longest = $length;
        }
        $i += $length;
    }
    return $longest;
}

因为这是一个有趣的练习,我在上面加了一个小班:

class Sequencer extends SplMaxHeap
{
    public function compare($a, $b) {
       return parent::compare(strlen($a), strlen($b));
    }
    public function key() {
        return strlen($this->current());
    }
    public function parseString($string)
    {
        $i = 0;
        $totalLength = strlen($string);
        while($i < $totalLength) {
            $length = strspn($string,  $string[$i], $i);
            $this->insert(str_repeat($string[$i], $length));
            $i += $length;
        }
    }
    public function getMaxLength()
    {
        $this->rewind();
        return strlen($this->top());
    }
}

那是一个 SplMaxHeap (需要5.3),这意味着您可以对它进行迭代,但这样做会从堆中提取元素,因此之后它将为空:

$sequencer = new Sequencer;
$sequencer->parseString('aaabbbbcccccddddddeeeeeeeffffffggggghhhhiiijjk');

echo $sequencer->getMaxLength(); // 7
foreach($sequencer as $length => $sequence) {
    echo "$length => $sequence\n";
}
echo $sequencer->getMaxLength(); // RuntimeException

迭代的结果将是

7 => eeeeeee
6 => dddddd
6 => ffffff
5 => ccccc
5 => ggggg
4 => hhhh
4 => bbbb
3 => iii
3 => aaa
2 => jj
1 => k

通过一次迭代字符串一个字符,跟踪最后一个击中的字符以及击中的次数,您可以非常轻松地得到这个结果。同时存储最大数量的字符;当您命中其他字符时,检查是否达到了新的最大连续字符数,如果达到了,则将其存储为新的最大连续字符数。当您遍历整个字符串时返回最大值。