Can't understand editorial

#1

Although i have done this question, through my way…
Not able to understand the editorial…

#2

In the editorial it is implemented through window sliding.
First of all say we want equal character of a only,then what we can do is while count of b is less than k it is okay as we can change b to a without using more than k changes.
As soon as count of b becomes greater than k(ie.k+1) we increment start till ‘b’ appears and then increase start again.
Same is done for b too.
eg.
“abbaa”
k=1
when we get the second b ie.at index 2(0-based)
we increase start till we get a b(ie.to 1st index) then increase start again to 2nd index.Now,count of b is 1 so for current window that ends with 2nd character,window size is 1.
similarly for other indexes.