title: How to match same length digits in a string using regex
body: <p>I want to find a text (for example: stack) in a String that contains digits and chars (for example: s123t123a123c123k). The only rule is that between every character of the search key there should be the same amount of digits, so all of this should match:</p>
  
  <pre><code>search key: stack
  
  Strings:
  stack                  //0 digit between chars of stack
  s7t3a9c0k              //1 digit between chars of stack
  s27t33a49c50k          //2 digit between chars of stack
  s127t312a229c330k      //3 digit between chars of stack and so on for 4,5,6 digits...
  </code></pre>
  
  <p>If I could match same length digits then I can write something like: s[]*t[]*a[]*c[]*k if the regex for same length digit is [].
  How to match same length digits in a string using regex?</p>