Recusrion and Dynamic Programming(DP)

Ways to approach:

• Bottom-up: Starting from the simplest case, then build a solution that on top of the previous one.
• Top-Down: The reverse of Bottom-up, less intuitive, but sometimes useful.
• Half-Half: They are usually seen on the bitwise operation and binary tree operation.

DP & memoization:

• Using recursion alone sometimes is not efficient enough, need to add Memoization to avoid doing repeat calculation.
• For recursion to work, a return on the base case is needed, so is what should be returned, is it the recursive function its self, the counter, or the result array?
• Find the pattern of recursion is the most important one.
• using an algorithm in a recursive way takes a lot of space, but doing the same algorithm in an iterative way is not easy sometimes, it's all about the trade-off.
• when naming variables on the matrix, put y at first, x at second, like this: matrix[y][x]