cerca nodo

def cercavalore(a, k):
    if a is None:
        return False

    if a.val == k:
        return True

    if a.sx is None a.dx is None:
        return False

    cercasx = False
    cercadx = False

    if a.sx is not None:
        cercasx = cercavalore(a.sx, k)

    if a.dx is not None:
        cercadx = cercavalore(a.dx, k)


    return cercasx or cercadx


def cercavalore2(a,k):
    if a is None:
        return False

    if a.val == k:
        return True

    return cercavalore2(a.sx,k) or cercavalore2(a.dx,k)