Replace Second Instance of String

Question

I just wondering how I could replace the second instance of a string inside a string in php such as follows:

a - b - c

Where it woulld add an extra space after the second "-" but only if it finds 2.

Answer 1

$finds = explode('-', "a - b - c");
if (count($finds) == 3) {
  $finds[2] = " {$finds[2]}";
}

$finds = implode('-', $finds);

Answer 2

$str ="a - b - c";    
if (substr_count($str,"-")>2){
  print preg_replace("/^(.*)-(.*)-(.*)/","\\1-\\2- \\3",$str);
}