Count number of ways to make MEX i for i in range [1,n+1]:

a) Only one way to make n+1

b) To make MEX 1, if l and r are min and max of locations of 1 in the two arrays, you must choose from range [1,l), (l,r), or (r , n] ( 1 indexed )

c) For every MEX ( other than 1 or n+1 ), keep track of the range of the previous MEXes (l and r unions of previous mexes) and find points such that l and r of previous mexes do no coincide with l and r of current number. Then merge the ranges!