title: Find number of binary numbers with certain constraints
body: <p>This is more of a puzzle than a coding problem. I need to find how many binary numbers can be generated satisfying certain constraints. The inputs are </p>
  
  <pre><code>(integer) Len - Number of digits in the binary number
  (integer) x
  (integer) y
  </code></pre>
  
  <p>The binary number has to be such that taking any x adjacent digits from the binary number should contain at least y 1's.</p>
  
  <p>For example -</p>
  
  <blockquote>
    <p>Len = 6, x = 3, y = 2</p>
    
    <p>0 1 1 0 1 1 - Length is 6, Take any 3 adjacent digits from this and
    there will be 2 l's</p>
  </blockquote>
  
  <p>I had this C# coding question posed to me in an interview and I cannot figure out any algorithm to solve this. Not looking for code (although it's welcome), any sort of help, pointers are appreciated</p>