title: largest complete subtree in a binary tree
body: <p>I am defining a complete subtree as a tree with all levels full and the last level left justified i.e. all nodes are as far left as possible, and I want to find the largest subtree in a tree that is complete.</p>
  
  <p>One method is to do the method outlined <a href="https://stackoverflow.com/a/20432173/3673043">here</a> for every node as root, which would take O(n^2) time.</p>
  
  <p>Is there a better approach?</p>