I would certainly recommend the Skiena book. You’ve started to learn about algorithms, you should start to learn algorithms too.
To whoever edited this answer and replaced the last occurrence of the word algorithms with the word mathematics: I meant algorithms when I wrote this answer, I still mean algorithms, replacing the word with mathematics materially changes the answer. If you think that mathematics is what OP should learn, post your own answer to that effect. If you had troubled to read the commentary below you would understand why I chose the word algorithms and not mathematics.