Program in C++ please comment in the program so I can understand the code. Given a string, s, and a list of words, words, that are all of the same length. Find all starting indices of substring(s) in s that is a concatenation of each word in words exactly once and without any intervening characters.

For example, given: s: "barfoothefoobarman" words: ["foo", "bar"] You should return the indices: [0,9]. (order does not matter).