For 4, I would recommend leetcode (or, others whichever suits you), and Algorithm Design Manual by Skiena. 2 activities that helped me greatly. Once you read a

For 4, I would recommend leetcode (or, others whichever suits you), and Algorithm Design Manual by Skiena. 2 activities that helped me greatly. Once you read and solve enough problems, then you will start noticing patterns while understanding their purpose.