$$
A = \begin{bmatrix}
a_{11} & a_{12} & … & a_{1n}\
a_{21} & a_{22} & … & a_{2n}\
a_{31} & a_{22} & … & a_{3n}\
\vdots & \vdots & \ddots & \vdots\
a_{n1} & a_{n2} & … & a_{nn}\
\end{bmatrix} , b = \begin{bmatrix}
b_{1} \
b_{2} \
b_{3} \
\vdots \
b_{n} \
\end{bmatrix}
$$
$O(n)$
https://kongshuilinhua.github.io/2025/01/01/test/