Merge Sort

The implementation(generalised ) of merge sort

QuickSort

Generalised QuickSort Code
Hoares and simple partition and Randomised Quick sort

Prime problems

Learn about prime number from any standard book or competitive programming book.then  try to code basic algorithms like sieve for finding prime then try KPRIME,PRIME1,LEVY,PPERM,RESQ on codechef these are very simple and interesting problem and also their editorial is avalable . So,that u can surely learn something. I will add some other problem title related in somedays.