title: Minimum number of cameras required to cover all nodes in graph
body: <p>I came across a problem in leetcode named "Binary Tree Camera". </p>
  
  <p>I was wondering how to approach this similar problem:- </p>
  
  <p>You have to place cameras at nodes of a graph such that whole graph is covered. A camera on a node monitors all its immediate neighbour nodes and itself. Find the minimum number of cameras required to cover all nodes.</p>