My own problem:
Let G be a undirected graph with $n$ vertex and $m$ edges.
We have a list that $v_{1} \rightarrow v_{2}$ but it's not important now.
Every edge has a weight equal to X.
Our task is to find all pairs $(v_i, v_j)$ that fastest path from $v_i $ to $v_j$ is about $w = 2X$.
(Look at example)
Create algorithm with $O(n^2)$ complexity, simlar or faster :)
Example:
$n = m = 5$
$ v_1 \rightarrow v_2 \rightarrow v_3 \rightarrow v_4 \rightarrow v_5$ and $v_1 \rightarrow v_3$
Solution:
$(1,4), (2,4), (3,5)$.
Picture:
Shortest path from $v_1$ to $v_4$ is 2X (the same with another solutions).
EDIT: we have adjacency List.