// Permutation in String — MEDIUM
// Category: sliding-window
Given two strings `s1` and `s2`, return `true` if `s2` **contains a permutation** of `s1`, or `false` otherwise.
In other words, return `true` if one of `s1`'s permutations is a substring of `s2`.
**Constraints:**
- `1 <= s1.length, s2.length <= 10⁴`
Example: s1 = "ab", s2 = "eidbaooo"
Output: true