4. Let G = (V,E) be a weighted, directed graph with weight function w: E 1-1,+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, antd 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. Last update September 6, 2017