#The solution provide is incorrect, do not calculate max_lenght in invalid windows, add else condition
# Current window size is from window_start to window_end, overall we have a letter
            # which is repeating 'max_repeat_letter_count' times, this means we can have a window
            # which has one letter repeating 'max_repeat_letter_count' times and the remaining
            # letters we should replace. If the remaining letters are more than 'k', it is the
            # time to shrink the window as we are not allowed to replace more than 'k' letters
            if (window_end - window_start + 1 - max_repeat_letter_count) > k:
                left_char = str1[window_start]
                frequency_map[left_char] -= 1
                window_start += 1
            else: 
			           max_length = max(max_length, window_end - window_start + 1)