Shortest paths are not always unique: sometimes there are two or more different paths
with the minimum possible length. Show how to solve the following problem in O(( |V | +
|E| ) log |V | ) time.
Input: An undirected graph G = (V, E); edge lengths le > 0; starting vertex s ∈S .
Output: A Boolean array usp[·]: for each node u, the entry usp[u] should be true if and
only if there is a unique shortest path from s to u. (Note: usp[s] = true.)