001package algs42;
002import stdlib.*;
003import algs13.Queue;
004import algs13.Stack;
005/* ***********************************************************************
006 *  Compilation:  javac BreadthFirstDirectedPaths.java
007 *  Execution:    java BreadthFirstDirectedPaths V E
008 *  Dependencies: Digraph.java Queue.java Stack.java
009 *
010 *  Run breadth first search on a digraph.
011 *  Runs in O(E + V) time.
012 *
013 *  % java BreadthFirstDirectedPaths tinyDG.txt 3
014 *  3 to 0 (2):  3->2->0
015 *  3 to 1 (3):  3->2->0->1
016 *  3 to 2 (1):  3->2
017 *  3 to 3 (0):  3
018 *  3 to 4 (2):  3->5->4
019 *  3 to 5 (1):  3->5
020 *  3 to 6 (-):  not connected
021 *  3 to 7 (-):  not connected
022 *  3 to 8 (-):  not connected
023 *  3 to 9 (-):  not connected
024 *  3 to 10 (-):  not connected
025 *  3 to 11 (-):  not connected
026 *  3 to 12 (-):  not connected
027 *
028 *************************************************************************/
029
030public class BreadthFirstDirectedPaths {
031        private static int INFINITY = Integer.MAX_VALUE;
032        private boolean[] marked;  // marked[v] = is there an s->v path?
033        private int[] edgeTo;      // edgeTo[v] = last edge on shortest s->v path
034        private int[] distTo;      // distTo[v] = length of shortest s->v path
035
036        // single source
037        public BreadthFirstDirectedPaths(Digraph G, int s) {
038                marked = new boolean[G.V()];
039                distTo = new int[G.V()];
040                edgeTo = new int[G.V()];
041                for (int v = 0; v < G.V(); v++) distTo[v] = INFINITY;
042                bfs(G, s);
043        }
044
045        // multiple sources
046        public BreadthFirstDirectedPaths(Digraph G, Iterable<Integer> sources) {
047                marked = new boolean[G.V()];
048                distTo = new int[G.V()];
049                edgeTo = new int[G.V()];
050                for (int v = 0; v < G.V(); v++) distTo[v] = INFINITY;
051                bfs(G, sources);
052        }
053
054        // BFS from single source
055        private void bfs(Digraph G, int s) {
056                Queue<Integer> q = new Queue<>();
057                marked[s] = true;
058                distTo[s] = 0;
059                q.enqueue(s);
060                while (!q.isEmpty()) {
061                        int v = q.dequeue();
062                        for (int w : G.adj(v)) {
063                                if (!marked[w]) {
064                                        edgeTo[w] = v;
065                                        distTo[w] = distTo[v] + 1;
066                                        marked[w] = true; // for BFS, mark as you enqueue
067                                        q.enqueue(w);
068                                }
069                        }
070                }
071        }
072
073        // BFS from multiple sources
074        private void bfs(Digraph G, Iterable<Integer> sources) {
075                Queue<Integer> q = new Queue<>();
076                for (int s : sources) {
077                        marked[s] = true;
078                        distTo[s] = 0;
079                        q.enqueue(s);
080                }
081                while (!q.isEmpty()) {
082                        int v = q.dequeue();
083                        for (int w : G.adj(v)) {
084                                if (!marked[w]) {
085                                        edgeTo[w] = v;
086                                        distTo[w] = distTo[v] + 1;
087                                        marked[w] = true;
088                                        q.enqueue(w);
089                                }
090                        }
091                }
092        }
093
094        // length of shortest path from s (or sources) to v
095        public int distTo(int v) {
096                return distTo[v];
097        }
098
099        // is there a directed path from s (or sources) to v?
100        public boolean hasPathTo(int v) {
101                return marked[v];
102        }
103
104        // shortest path from s (or sources) to v; null if no such path
105        public Iterable<Integer> pathTo(int v) {
106                if (!hasPathTo(v)) return null;
107                Stack<Integer> path = new Stack<>();
108                int x;
109                for (x = v; distTo[x] != 0; x = edgeTo[x])
110                        path.push(x);
111                path.push(x);
112                return path;
113        }
114
115        public static void main(String[] args) {
116                args = new String[] { "data/tinyDG.txt", "3" };
117
118                In in = new In(args[0]);
119                Digraph G = DigraphGenerator.fromIn(in);
120                // StdOut.println(G);
121
122                int s = Integer.parseInt(args[1]);
123                BreadthFirstDirectedPaths bfs = new BreadthFirstDirectedPaths(G, s);
124
125                for (int v = 0; v < G.V(); v++) {
126                        if (bfs.hasPathTo(v)) {
127                                StdOut.format("%d to %d (%d):  ", s, v, bfs.distTo(v));
128                                for (int x : bfs.pathTo(v)) {
129                                        if (x == s) StdOut.print(x);
130                                        else        StdOut.print("->" + x);
131                                }
132                                StdOut.println();
133                        }
134
135                        else {
136                                StdOut.format("%d to %d (-):  not connected\n", s, v);
137                        }
138
139                }
140        }
141
142
143}