Solution (source code)

= Solution

For $x\alpha+y\beta$, the simple-coroot coordinates are $2x-y$ and $-3x+2y$. Solving for the <fundamental weights> gives
$$
\chi=2\alpha+3\beta,
\qquad
\omega=\alpha+2\beta.
$$
Hence $C_1=2$, $C_2=3$, and $C_3=2$. The weight $\omega$ is the fundamental weight of the short root, and its <highest-weight representation> is the seven-dimensional fundamental representation of $G_2$. Its weights are zero and the six short roots.