Q:

Find and replace duplicates in Array

I need to make app with will fill array with some random values, but if in array are duplicates my app not working correctly. So I need to write script code which will find duplicates and replace them with some other values.
Okay so for example i have an array:
<?PHP
$charset=array(123,78111,0000,123,900,134,00000,900);

function arrayDupFindAndReplace($array){

// if in array are duplicated values then -> Replace duplicates with some other numbers which ones I'm able to specify.
return $ArrayWithReplacedValues;
}
?>

So result shall be the same array with replaced duplicated values.

A:

You can just keep track of the words that you've seen so far and replace as you go.
// words we've seen so far
$words_so_far = array();
// for each word, check if we've encountered it so far
//    - if not, add it to our list
//    - if yes, replace it
foreach($charset as $k => $word){
    if(in_array($word, $words_so_far)){
        $charset[$k] = $your_replacement_here;
    }
    else {
        $words_so_far[] = $word;
    }
}

For a somewhat-optimized solution (for cases where there are not that many duplicates), use array_count_values() (reference here) to count the number of times it shows up. 
// counts the number of words
$word_count = array_count_values($charset);
// words we've seen so far
$words_so_far = array();
// for each word, check if we've encountered it so far
//    - if not, add it to our list
//    - if yes, replace it
foreach($charset as $k => $word){
    if($word_count[$word] > 1 && in_array($word, $words_so_far)){
        $charset[$k] = $your_replacement_here;
    }
    elseif($word_count[$word] > 1){
        $words_so_far[] = $word;
    }
}

