Counting in Base B

You are given arrays $L$ and $R$, each of size $N$, denoting numbers in base $B$ representation. Count the number of arrays of size $N$ such that: - The array denotes a number in base $B$ representation; - The number denoted by the array lies between $L$ and $R$ (both inclusive); - There are exactly $K$ distinct elements in the array. Since the answer may be large, output it modulo $10^9 + 7$.