[numpy] count unique element

def count_unique(a):
    q = np.zeros(5000000, dtype=int)
    q[a.ravel()] = 1
    v = np.nonzero(q)[0]
    return v


a = np.random.randint(1, 256, size=300000)
q = np.zeros(512, dtype=int) # or some big number (bigger than the list)
q[a.ravel()] = 1
v = np.nonzero(q)[0]
u = np.unique(a)
np.array_equlas(u, v)