Unique Input/Output (UIO) sequence is an efficient method to perform functional test of Finite State Machine (FSM)

which arises in many applications

such as VLSI designs and communication protocols

etc.A heuristic algorithm based on Distinguished State Group (DSG) is described to generate UIO sequences.The optimizing methods include a hellristic strategy based on a specific 'less’ relation

several pruning strategies

and a novel access mechanism of multiple OPEN/CLOSED lists

and these methods eliminate ono-sense nodes and branches to a great extent.According to the experimental results

the practicability of all the measures is analyzed.Compared with brute algorithms

the optimized one is improved in terms of time and space complexities.