title: regular expression of a binary string of odd length and 0 as the middle symbol
body: <p>regular expression of a binary string of odd length and <code>0</code> as the middle symbol. having trouble in figuring out how to maintain having a 0 in the middle. (left part made up of binary numbers + <code>0</code> + same as the left part). so far i made it till <code>((01)(0+1)*0)U((01)(0+1)*)</code>, but still wrong. only able to use <code>+</code>, <code>*</code> and <code>U</code></p>