1. You use one array with 2 different columns, such as 0,0 and 0,1 then 1,0 and 1,1 where 0 is the X co-ord and 1 is the Y co-ords, you would push back X and then Y you need to set in the same row and for this you need to know the row's X value so use the array's width to work it out maybe array.width-1,1, where the X is set at array.width-1,0 when you push it
2. You can pop the top row of the array as you push one in