  We prove that the multiplicities of certain maximal weights of
$\mathfrak{g}(A^{(1)}_{n})$-modules are counted by pattern avoidance on words.
This proves and generalizes a conjecture of Misra-Rebecca. We also prove
similar phenomena in types $A^{(2)}_{2n}$ and $D^{(2)}_{n+1}$. Both proofs are
applications of Kashiwara's crystal theory.
