The divide and conquer strategy involves breaking down a problem into multiple independent subproblems, solving the subproblems (recursively), and combining those solutions into a solution for the original problem.
If the original problem is broken down into a single subproblem, it is called a decrease and conquer strategy, and is very efficient to solve (via tail recursion or a simple loop).
To analyze the complexity of these things, you'll generally need to solve recurrence relations.
Implementation of these is left as an exercise for you: