The correct combinations of Buddhist philosophical schools and their respective thinkers are:
(a) Mādhayamika is associated with (ii) Nāgārjuna, as Nāgārjuna was the founder of the Mādhayamika school, emphasizing the philosophy of emptiness (it{śūnyatā}).
(b) Yogācāra is associated with (i) Vasubandhu, who, along with Asaṅga, was a prominent proponent of the Yogācāra or the "mind-only" school.
Incorrect options:
(c) Sarvāstivāda and (iii) Sariputta (Śāriputra): Sarvāstivāda was not directly associated with Śāriputra.
(d) Sautrāntika and (iv) Ānanda: Sautrāntika is not primarily linked with Ānanda.
Thus, the correct matches are (a) Mādhayamika → Nāgārjuna and (b) Yogācāra → Vasubandhu.