Hamming Distance of Constacyclic Codes of Length <italic>p<sup>s</sup></italic> Over F<sub><italic>p<sup>m</sup></italic></sub>+<italic>u</italic>F<sub><italic>p<sup>m</sup></italic></sub>+<italic>u</italic>²F<sub><italic>p<sup>m</sup></italic></sub>
Let $p$ be any prime, $s$ and $m$ be positive integers. In this paper, we completely determine the Hamming distance of all constacyclic codes of length $p^s$ over the finite commutative chain ring $\mathbb {F}_{p^m}+ u\mathbb {F}_{p^m} + u^{2}\mathbb {F}_{p^m}\,\,\, (u^3=0)$ . As applications, we identify all maximum distance saparable codes (i.e., optimal codes with respect to the Singleton bound) among them.