Below is the syntax highlighted version of Bridge.java
from §4.1 Undirected Graphs.

/****************************************************************************** * Compilation: javac Bridge.java * Execution: java Bridge V E * Dependencies: Graph.java GraphGenerator.java * * Identifies bridge edges and prints them out. This decomposes * a directed graph into two-edge connected components. * Runs in O(E + V) time. * * Key quantity: low[v] = minimum DFS preorder number of v * and the set of vertices w for which there is a back edge (x, w) * with x a descendant of v and w an ancestor of v. * * Note: code assumes no parallel edges, e.g., two parallel edges * would be (incorrectly) identified as bridges. * ******************************************************************************/ public class Bridge { private int bridges; // number of bridges private int cnt; // counter private int[] pre; // pre[v] = order in which dfs examines v private int[] low; // low[v] = lowest preorder of any vertex connected to v public Bridge(Graph G) { low = new int[G.V()]; pre = new int[G.V()]; for (int v = 0; v < G.V(); v++) low[v] = -1; for (int v = 0; v < G.V(); v++) pre[v] = -1; for (int v = 0; v < G.V(); v++) if (pre[v] == -1) dfs(G, v, v); } public int components() { return bridges + 1; } private void dfs(Graph G, int u, int v) { pre[v] = cnt++; low[v] = pre[v]; for (int w : G.adj(v)) { if (pre[w] == -1) { dfs(G, v, w); low[v] = Math.min(low[v], low[w]); if (low[w] == pre[w]) { StdOut.println(v + "-" + w + " is a bridge"); bridges++; } } // update low number - ignore reverse of edge leading to v else if (w != u) low[v] = Math.min(low[v], pre[w]); } } // test client public static void main(String[] args) { int V = Integer.parseInt(args[0]); int E = Integer.parseInt(args[1]); Graph G = GraphGenerator.simple(V, E); StdOut.println(G); Bridge bridge = new Bridge(G); StdOut.println("Edge connected components = " + bridge.components()); } }

Last updated: Fri Oct 20 12:50:46 EDT 2017.