This shorts and wall is proving effective. I can revise things, and write more in english.

Two problems one of which could solve and one I couldn’t.

1. Longest Repeating Character Replacement
2. Sliding Window Maximum

Most of the substring problem require a window. Although its a trap, because sometimes its not a slider, the window-ing is there, but maybe some data can be reused later.

1. Longest Repeating Character Replacement

Here the property is within a given window, there would be some repeating characters, one of which will be the largest, and for the window to be valid the invariant would be:

• length of the window - the maximum count of the unique character <= to k (given replacements allowed)

• Init: window len = 0, max count = 0 so, w - m <= k, is true
• Body: add characters to the window, computing the maxFreq, then make sure the invariant is true, which is (w - m) > k, reduce the window, reducing the counter.
• End: once the window is valid again, we compute the maxLen of the window