http://www.geeksforgeeks.org/fundamentals-of-algorithms/ This page has a lot of algorithms with implementation and tutorials, ranging from beginner to intermediate stuff. When you master the basic stuff (or right now if you feel confident!), you can purchase the Competitive Programming Book by Steven and Felix Halim, it teaches really well how to solve a lot of problems that are recurrent in ACM ICPC and IOI, this is my team's main source of study.

I am not an expert but I have read some of the editorials from the websites given below and found them helpful.

1. Topcoder

2. Code Monk

3. Codechef

4. As skavurskaa suggested, GeeksforGeeks

5. Topcoder SRM Editorial

Books

1. CLRS

2. Competitive Programming 3

Personally, I found Topcoder data science tutorials pretty good. Topcoder Data Science Tutorial