How to mark in bold triple and quadrupled sequential characters of a string?

Question

I want to mark the triple and quadrupled sequences of a string like this:

$string = "AAACDEAAAABBBUUDD";

And I would like to get as a result the following:

<b>AAA</b>CDE<b>AAAA</b><b>BBB</b>UUDD

Answer 1

PHP version

   $string = 'AAACDEAAAABBBUUDD';
   $bold = preg_replace( '/(.)\1{2,}/', '<b>$0</b>' , $string );

See working on IDEONE

Javascript version

var str = "AAACDEAAAABBBUUDD";
var res = str.replace( /(.)\1{2,}/g, "<b>$&</b>");

See working on IDEONE

Understanding the Regex

• (.) = any character (switch to (\S) if you don’t want spaces);

• \1 = the character referred to above by the first group (.);

• {2,} two or more occurrences of the preceding character. If you only want sequences of three or four characters, disregarding five or more, replace with {2,3} (original plus two equals, or original plus three equals).

That is, with each iterated character, we check if it is followed by 2 more occurrences of the same, totaling the 3 or more desired.

The substitution <b>$0</b> ($& in JS) takes the whole set found, and adds the Bold.