Figure shows the evolution of the cumulative number of unique hit molecules that reached the target region against the number of steps. The left panel shows the cumulative number of hits as a function of the total number of molecules generated. This is a different view of the results in Figure . It was confirmed that SMC-RECUR-GTM is the most efficient method to find molecules hidden in the target region. It was also confirmed that SMC-RECUR-GTM-SR-PL has a reduced hit rate due to the use of the surrogate models involving approximation errors, as mentioned above. Vanilla SMC-2 and SMC-3 also consistently found the target molecules. This suggests that it is difficult to fully cover the large design space with as few as T × m = 500000 search trials. The right panel in Figure shows the cumulative number of hits per step as a function of execution time (right panel). In terms of computational cost, the parallel recursive molecular design algorithm SMC-RECUR-GTM-SR-PL with the surrogate models showed by far the highest search efficiency. With regard to the results for scenario 2: The number of hit molecules at each step (Figure ) and the cumulative number of hits (Figure ) were significantly lower for the two random searches, as in scenario 1. In contrast to the results of scenario 1, SMC-1 and Random, whose design space was restricted to single-step reactions with two reactants, did not show any decay in the number of hit molecules throughout all steps. This observation indicates that, as the number of commercial reactants increases, the design space becomes much larger, even for single-step reactions. Among the methods other than the random searches, no significant difference was found in the evolution of the number of hit molecules and the cumulative number. However, similar to the results of scenario 2, SMC-RECUR-GTM-SR-PL showed by far the highest search efficiency in terms of the number of hit molecules per execution time (right panel in Figure ). From a practical point of view, search performance against execution time is considered the most important criterion. Therefore, we conclude that SMC-RECUR-GTM-SR-PL is superior in terms of the evaluation criteria for detecting the number of unique molecules.