问在PHP数组中查找和替换多行短语/文本而不损坏数组

EN

$myarray = [
    0 => 'Johnny likes to go to school',
    1 => 'but he only likes to go on Saturday',
    2 => 'because Saturdays are the best days',
    3 => 'unless you of course include Mondays',
    4 => 'which are also pretty great days too.',
    5 => 'Sometimes Johnny likes picking Strawberrys',
    6 => 'with his mother in the fields',
    7 => 'but sometimes he likes picking blueberries'
];

// preg_quote this because we're looking for the string, not for a pattern it might contain
$findstring = preg_quote("Sundays which are also pretty good");
// htmlentities this in case it contains a string of characters which happen to be an html entity
$replacestring = htmlentities("Mondays which are also pretty great");

// Combine array into one string
// We use htmlentitles to escape the ampersand, so we can use it as a sentence delimeter
$mystring = implode("&", array_map('htmlentities', $myarray));

// Turns $findString into:
// S\&?u\&?n\&?d\&?a\&?y\&?s\&? \&?w\&?h\&?i\&?c\&?h\&? \&?a\&?r\&?e\&?
// \&?a\&?l\&?s\&?o\&? \&?p\&?r\&?e\&?t\&?t\&?y\&? \&?g\&?o\&?o\&?d
$regexstring = implode("\&?", str_split($findstring));

// Johnny likes to go to school&but he only likes to go on Saturday&because Saturdays are the
// best days&unless you of course include Mondays&which are also pretty great days
// too.&Sometimes Johnny likes picking Strawberrys&with his mother in the fields&but sometimes
// he likes picking blueberries
$finalstring = preg_replace("/$regexstring/", $replacestring, $mystring);

// Break string back up into array, and return any html entities which might have existed
// at the beginning.
$replacedarray = array_map('html_entity_decode', explode("&", $finalstring));

var_dump($replacedarray);