gistfile1.txt

role1 = { name, perms: [p1, p2, p3] }
role2 = { name, perms: [p3, p4] }
roles = [role1, role2, ...]

# put lists in sorted sort
# O(N_roles * N_permissions log N_permissions)
roles.forEach { sortInPlace(_.perms) }

# compare each role to the other, N^2 = 16m comparison
# perms overlap is O(N_perms) = O(300)
# 16m * 300 == still doabled
roles.each { r1 => 
  roles.each { r2 =>
    intersect(r1.perms, r2.perms)
  }
}

intersect(l1, l2) {
  // https://www.geeksforgeeks.org/intersection-of-two-sorted-linked-lists/
}