code: public double getSizeOfLevel(int level) {
  		checkArg(level >= 0, "level must be >= 0");
  		checkArg(level < getLevelCount(), "level must be < levelCount");
  
  		return sizeOfLevel.get(level);
  	}
docs: Returns the size of a level.
  <p>
  When the root is located at the top or bottom the size of a level is the
  maximal height of the nodes of that level. When the root is located at
  the left or right the size of a level is the maximal width of the nodes
  of that level.
  
  @param level &nbsp;
  @return the size of the level [level &gt;= 0 &amp;&amp; level &lt; levelCount]