you have a grid of lights. each light is initially either off or on. every column in the grid has a switch and when the switch is flipped, all the lights in that column reverse states given a array q of strings, where the j-th character of the i-th element is 'y' if the light in row i, column j is initially on, and 'n' otherwise, find the largest number of rows that can be lit after performing exactly m flips a row in the grid is considered lit if all the lamps in that row are on and m flips do not necessarily have to be on m distinct switches