Problems and it's solutions. 
Problem solving, a great Speed comes with a good Accuracy. The more Accurate you can write code, the more Speed you will gain.
Now, Accuracy comes with solving problems! Please read the contribution guidline!
So, here presented before you a repository housing the largest collection of problems (and their solutions, of course). Make this the one and only repository where people can turn to when they want to practice problem solving and if somebody is stuck in some programming problem in some coding contest. But, I don't encourage you to look at the solution right away. First understand the problem, do some brainstorming and if you still can't solve, go for the solution!
Make sure you also contribute to this repo by adding different problems and their solutions too. We encourage solutions in different languages too!
Files are grouped by language for a more organized search:
There are various websites which focus on the skills of problem solving. A few of them, namely, have all the challenges you have been craving for:
The best advice when it comes algorithms is grinding continuously - until they seem simpler.
Before you can get your hands dirty in solving algorithm challenges, you can learn a lot about Data Structures and Algorithms. Some good source for learning it :