Given strings *s1* and *s2*, return `true` if *s2* contains any permutation of *s1* as a substring. Otherwise, return `false`. (Sliding window + two-pointer with hash).
Two lines: s1, then s2.
"true" or "false".
Example 1:
Input:
s1 = "ab" s2 = "eidbaooo"
Output:
true
Explanation:
"ba" is a permutation of "ab" and appears in s2.