Problem: Substring with Concatenation of All Words

Statement

You are given a string s and an array of strings words, where every string in words has the same length.

A concatenated string is formed by taking any permutation of words and concatenating all the strings in that permutation together. In other words, it is a string that contains every element of words exactly in the order defined by some permutation, with no extra characters.

Return a list of all starting indices in s where a substring that is a concatenated string begins. The answer may be returned in any order.

Note: The array words may contain duplicate strings.

Constraints:

• $1 \leq$ s.length $\leq 10^4$

• $1 \leq$ words.length $\leq 5000$

• $1 \leq$ words[i].length $\leq 30$ ...