Permission bitmask encoder

An access-control service stores each user's permissions as one integer bitmask. You are given the ordered list of permission names for a resource — the name at index i corresponds to bit i — and the list of names granted to a user (each granted name appears in the flag list; no duplicates). Return the bitmask encoding the grant. For example, with flags ["read", "write", "delete"] and granted ["read", "delete"], bits 0 and 2 are set, so return 5.