best way to recognize this pattern?

i want to recognize a pattern, just a list of four double numbers. say List (L) e.g. 0,3,1,2

the criteria is ,

L[1] > L[0]
L[2] < L[1] and L[2] > L[0]
L[3] < L[1]

it's like a sin wave, i want to know if there's a simple way to do above iterative check, something like a FFT ? but just for a series of 4 numbers, it's not so beneficial to use transforms.

thanks