Let G = (V, E) be a weighted, directed graph with weight function w: E {1, +1}. The weight w(p) of a path p is the sum of all edge weights in the path. We say a path p is a Z-path iff its path weight w(p) is 0, and any positive edge (i.e., the edge with +1 weight) appears after all negative edges (i.e., the edges with 1 weights) in path p. For example, the path 1, 1, +1, +1 is a Z-path but 1, +1, 1, +1 is not. A node v in V is Z-path-reachable from node u iff there is a Z-path p from u to v in G. Give an O(EV )-time algorithm compute the all Z-path-reachable node pairs in the digraph G. Note that the graph can contain negative cycles.