Past exam of the short options course of the University of Oxford / 2023 / 7 / a / ii / Solution

A shortest-path tree rooted at $x$ is a spanning tree $T$ such that, for every vertex $v$, the unique $xv$ graph path in $T$ has minimum total edge length among all $xv$ graph paths in $G$. The objective is the sum of the lengths along each route, not the sum of all the tree's edge lengths.