Find All Anagrams in a String

Statement

Given two strings, a and b, return an array of all the start indexes of anagrams of b in a. We may return the answer in any order.

An anagram is a word or phrase created by rearranging the letters of another word or phrase while utilizing each of the original letters exactly once. For example, “act” is the anagram of “cat”, and “flow” is the anagram of “wolf”.

Constraints:

• $1\leq$ a.length, b.length $\leq 10^3$
• Both a and b consist only of lowercase English letters.