Python 2, 77 72 65 bytes
lambda a:map([len(set(t))for t in zip(*[iter(a)]*3)].count,(1,2))
7 bytes saved via a clever trick from xnor
lambda a:map([len(set(t))for t in zip(*[iter(a)]*3)].count,(1,2))
7 bytes saved via a clever trick from xnor