Now we test the window
One pointer/index corresponds to the beginning of your window, and the other corresponds to the end of the window. The first step is to move one pointer to find a valid window. This happens as we iterate through each letter, and run it through the following code block.
1// continue running while there's more elements in `s` to process
2if (s[end] in hash) { // we've found a letter we needed to fulfill
3
4 // modify the length counter, we can use this as part of our substring
5 if (hash[s[end]] > 0) {
6 counter -= 1;
7 }
8
9 // modify the dictionary to say we've gotten this character requirement
10 hash[s[end]] -= 1;
11}
12
13// Keep expanding the window once we are done contracting, try more substrings
14end += 1