title: find minimum dominating set in a binary tree
body: <p>QUESTION: On clicking a node in a tree, all the adjacent edges that are connected to that node, are turned on. Calculate minimum number of clicks such that all the edges are turned on.</p>
  
  <p>This a interview question which was asked to my friend in some interview, To solve this problem First i thought to do level-order traversal and click nodes at alternate levels, if a leaf is found at current selected level, click on its parent instead of leaf in order to make no of clicks minimum.  </p>
  
  <p>But above solution doesn't work for all binary tree structure and giving more no of clicks while even lesser no of clicks can also turn on all the edges.</p>
  
  <p>After searching it on the net, i got to know its a kind of finding minimum Dominating set in a binary tree. 
  Please suggest some way to solve this problem efficiently.</p>