Online judges are often used in programming education for beginners. Although they help improve coding skills, students may not obtain sufficient educational effects with much assignment difficulty. Instead of presenting a model answer to an assignment, we propose an approach to provide students contents of problems and answer source code similar to the assignment. We implemented the approach as a system and conducted an intervention experiment in a university lecture course to evaluate its effectiveness. There was a statistically significant improvement in the number of correct answers compared to the same course in another year without the proposed system. Therefore, it is suggested that the proposed approach can aid in the understanding of an assignment and improve the educational effect.