So, for new people, I'm doing leetcode for a long time. And sometimes I'm pasting here useful templates / approaches for leetcode questions (as they are needed for interview).

Today given good 2dp problem we will see how to convert top-down to bottom up (without applying much thinking).

1. Come up with exponential recursion that has input and produces (stateless) output for it
2. Add memoization with @cache decorator
3. Apply array based cache (-1 element does not exist)

4. Slightly imagine the callstack of recursion, and reverse it with for loop.
4.1 Depending on your recursion, realize where input starts, where it ends. In our case we start from 0,0 and end at len(s1) or len(s2). So for bottom up we should reverse -> we start from len(s1) & len(s2) and go up from bottom to 0,0.
4.2 Create these reversed for loops
4.3 Check base cases, and precalculate base cases before for loop
4.4 All remaining code is the same as in top down except (return ans). Change recursive calls to cache calls

5. You are welcome