X289: Structurally Identical Binary Trees Exercise

Given two binary trees, return true if and only if they are structurally identical (they have the same shape, but their nodes can have different values).
Here are methods that you can use on the BinNode objects:
   interface BinNode {
      public int value();
      public void setValue(int v);
      public BinNode left();
      public BinNode right();
      public boolean isLeaf();
   }