printHeap method

Implementation

@override
String printHeap() {
  final buffer = StringBuffer();
  buffer.writeln('--- MaxHeap<$T> (size=$size) ---');
  buffer.writeln('| val |');
  buffer.writeln('|-----|');
  for (final val in _heap) {
    buffer.writeln('| $val |');
  }
  buffer.writeln('--- End of Heap ---');
  return buffer.toString();
}