Yeah, this is just a skill issue that is solvable with practice. You need to develop a proper intuition on what is actually happening both at the algorithm abstraction level, and the language level so you can express a solution fluently. If you have not studied a lot it is difficult to internalize what tools are in your toolbox that would help you. This includes patterns, abstractions, language features, libraries, and more. The only thing that fixes this is practice reaching for those tools until they feel natural. Keep practicing with the book reference because that is closer to reality than not. But at a certain point you should be able cogently write simple programs from scratch without referencing materials in at least one language.