Edit Distance (Levenshtein Distance)

You are given two strings $s_1$ and $s_2$. You can transform $s_1$ into $s_2$ using three operations, each costing 1: - **Insert** a character at any position - **Delete** a character at any position - **Substitute** one character for another Write a function that returns the minimum total number of operations needed to convert $s_1$ into $s_2$. This quantity is known as the Levenshtein (edit) distance. **Constraints:** - $0 \leq |s_1|, |s_2| \leq 500$ - Both strings consist of lowercase English letters **Examples:** 1. `s1 = "kitten"`, `s2 = "sitting"` → `3` - kitten → sitten (substitute 'k' with 's') - sitten → sittin (substitute 'e' with 'i') - sittin → sitting (insert 'g' at end) 2. `s1 = "horse"`, `s2 = "ros"` → `3` - horse → rorse (substitute 'h' with 'r') - rorse → rose (delete 'r') - rose → ros (delete 'e') 3. `s1 = ""`, `s2 = "abc"` → `3` (3 insertions)