php字符串反转 面试中经常遇到的问题

1.单字节字符串反转

php提供了用于字符串反转的函数strrev()

$str = 'abcdef';

echo strrev($str);

2.对于包含中文的多字节字符串需要用到mb_substr()

$str = '字符串反转';

function rev($str, $encoding = 'utf-8'){

$len = mb_strlen($str);

$result = '';

for ($i = $len-1; $i>=0; $i--){

$result.= mb_substr($str,$i,1,$encoding);

}

return $result;

}

echo rev($str);

3.算法实现 首位交换

$str = 'abcdefg';

$len = strlen($str);

$times = $len/2;

for($i = 0;$i <= $times; $i++ ){

$tmp = $str[$i];

$str[$i] = $str[$len-$i-1];

$str[$len-$i-1] = $tmp;

}

echo $str;