  In this letter we present a flat histogram algorithm based on the pruned and
enriched Rosenbluth method (PERM). This algorithm incorporates in a
straightforward manner microcanonical reweighting techniques, leading to "flat
histogram" sampling in the chosen parameter space. As an additional benefit,
our algorithm is completely parameter free and, hence, easy to implement. We
apply this algorithm to interacting self-avoiding walks (ISAW), the generic
lattice model of polymer collapse.
