I'm not familiar with Grokking Algorithms, but fwiw the most important prereq at UIUC for 374 is 173, which also happens to have a free textbook[1] written by another UIUC professor, Margaret Fleck. I consider it to be a high quality introduction to discrete math and have good memories of her as a professor as well.

[1] https://mfleck.cs.illinois.edu/building-blocks/updates-fa201...