You are given a string `s` and an array of strings `words` of the same length. Return all starting indices of substring(s) in `s` that is a concatenation of each word in `words` exactly once, in any order, and without any intervening characters.

You can return the answer in any order.

Example 1:

    Input: s = "barfoothefoobarman", words = ["foo","bar"]
    Output: [0,9]
    Explanation: Substrings starting at index 0 and 9 are "barfoo" and "foobar" respectively.
    The output order does not matter, returning [9,0] is fine too.

Example 2:

    Input: s = "wordgoodgoodgoodbestword", words = ["word","good","best","word"]
    Output: []

Example 3:

    Input: s = "barfoofoobarthefoobarman", words = ["bar","foo","the"]
    Output: [6,9,12]

Constraints:

- `1 <= s.length <= 104`
- `s` consists of lower-case English letters.
- `1 <= words.length <= 5000`
- `1 <= words[i].length <= 30`
- `words[i]` consists of lower-case English letters.