Project Euler is a problem solving challenge website where new problems are posted each week. A problem is often mathematically inspired and the answer is always a single number. To find this number you need to write an efficient algorithm.
I have currently solved this many problems:
I have benchmarked my solutions in both time and memory. Project Euler states that each problem is solvable in less than a minute with the right algorithm. As you can see most of my problems fulfill this requirement, with only a few problematic problems.