Given that the publisher, Springer, is giving it away for free during the pandemic, you should grab the PDF of Steven Skiena's The Algorithm Design Manual[0] (direct PDF link[1]) -- it's a book that has often been mentioned favorably here on HN.

(And you can pick up another book of his, The Data Science Design Manual[2] (direct PDF link[3]), which is similar in its conversational style, but about a different aspect of CS)

[0] https://link.springer.com/book/10.1007/978-1-84800-070-4

[1] https://link.springer.com/content/pdf/10.1007%2F978-1-84800-...

[2] https://link.springer.com/book/10.1007/978-3-319-55444-0

[3] https://link.springer.com/content/pdf/10.1007%2F978-3-319-55...