Design patterns are important in software maintenance because they help in designing, in understanding, and in re-engineering programs. The identification of occurrences of a design pattern consists in identifying, in a program, classes which structure and organisation match-strictly or approximately-the structure and organisation of classes as suggested by the design pattern. We express the problem of design pattern identification with operations on finite sets of bit-vectors. We use the inherent parallelism of bit-wise operations to derive an efficient bit-vector algorithm that finds exact and approximate occurrences of design patterns in a program. We apply our algorithm on three smallto- medium size programs, JHotDraw, Juzzle, and QuickUML, with the Abstract Factory and Composite design patterns and compare its performance and results with two existing constraint-based approaches.