3. Give an example of a simple directed, weighted graph G = (V, E, w: E \rightarrow \mathbb{R}) and
vertices s, t \in V such that Dijkstra's algorithm started at s does not find the shortest
s \rightarrow t path. Hint: You will need to use negative edge weights. (Note: this shows that
for finding shortest paths, the greedy choice property fails in the presence of negative
edge weights. Do you see why?)