The problem of automated feedback generation for introductory programming assignments (IPAs) has attracted significant attention with the increasing demand for programming education. While existing approaches, like \textit{Refactory}, that employ the \textit{"block-by-block"} repair strategy have produced promising results, they suffer from two limitations.

	First, \textit{Refactory} randomly applies refactoring and mutation operations to correct and buggy programs, respectively, to align their control-flow structures (CFSs), which, however, has a relatively low success rate and often complicates the original repairing tasks. 































































































































































































































































































































































































































































































































	Second, \textit{Refactory} generates repairs for each basic block of the buggy program when its semantics differs from the counterpart in the correct program, which, however, ignores the different roles that basic blocks play in the programs and often produces unnecessary repairs.































































































































































































































































































































































































































































































































	To overcome these limitations, we propose the \textsc{Brafar} approach to feedback generation for IPAs. 































































































































































































































































































































































































































































































































	The core innovation of \textsc{Brafar} lies in its novel bidirectional refactoring algorithm and coarse-to-fine fault localization.































































































































































































































































































































































































































































































































	The former aligns the CFSs of buggy and correct programs by applying semantics-preserving refactoring operations to both programs in a guided manner,































































































































































































































































































































































































































































































































	while the latter identifies basic blocks that truly need repairs based on the semantics of their enclosing statements and themselves.































































































































































































































































































































































































































































































































	In our experimental evaluation on 1783 real-life incorrect student submissions from a publicly available dataset, \textsc{Brafar} significantly outperformed \textit{Refactory} and \textsc{Clara}, generating correct repairs for more incorrect programs with smaller patch sizes in a shorter time.