001package algs41;
002import stdlib.*;
003import algs13.Stack;
004/* ***********************************************************************
005 *  Compilation:  javac DepthFirstPaths.java
006 *  Execution:    java DepthFirstPaths G s
007 *  Dependencies: Graph.java Stack.java StdOut.java
008 *  Data files:   http://algs4.cs.princeton.edu/41undirected/tinyCG.txt
009 *
010 *  Run depth first search on an undirected graph.
011 *  Runs in O(E + V) time.
012 *
013 *  %  java Graph tinyCG.txt
014 *  6 8
015 *  0: 2 1 5
016 *  1: 0 2
017 *  2: 0 1 3 4
018 *  3: 5 4 2
019 *  4: 3 2
020 *  5: 3 0
021 *
022 *  % java DepthFirstPaths tinyCG.txt 0
023 *  0 to 0:  0
024 *  0 to 1:  0-2-1
025 *  0 to 2:  0-2
026 *  0 to 3:  0-2-3
027 *  0 to 4:  0-2-3-4
028 *  0 to 5:  0-2-3-5
029 *
030 *************************************************************************/
031
032public class DepthFirstPaths {
033        private final boolean[] marked; // marked[v] = is there an s-v path?
034        private final int[] edgeTo;     // edgeTo[v] = last edge on s-v path
035        private final int s;            // source vertex
036
037        public DepthFirstPaths(Graph G, int s) {
038                this.s = s;
039                edgeTo = new int[G.V()];
040                marked = new boolean[G.V()];
041                dfsLoop (G, s);
042        }
043
044        // depth first search from v
045        private void dfs(Graph G, int v) {
046                //StdOut.format ("visited %d\n", v);
047                marked[v] = true;
048                for (int w : G.adj(v)) {
049                        if (!marked[w]) {
050                                edgeTo[w] = v;
051                                dfs(G, w);
052                        }
053                }
054        }
055        private void dfsLoop(Graph G, int s) {
056                Stack<Integer> stack = new Stack<>();
057                stack.push(s);
058
059                while (!stack.isEmpty()) {
060                        int v = stack.pop();
061                        marked[v] = true; // For DFS, mark as you pop
062                        for (int w : G.adj(v)) {
063                                if (!marked[w]) {
064                                        edgeTo[w] = v;
065                                        stack.push(w);
066                                }
067                        }
068                }
069        }
070        private void dfsLoopReversed(Graph G, int s) {
071                Stack<Integer> stack = new Stack<>();
072                stack.push(s);
073
074                while (!stack.isEmpty()) {
075                        int v = stack.pop();
076                        marked[v] = true;
077
078                        // tmp is used to get the vertices in the same order as used by the recursive version
079                        // tmp is not necessary, if you don't care about the order
080                        Stack<Integer> tmp = new Stack<>();
081                        for (int w : G.adj(v)) {
082                                if (!marked[w]) {
083                                        edgeTo[w] = v;
084                                        tmp.push(w);
085                                }
086                        }
087                        while (!tmp.isEmpty ())
088                                stack.push (tmp.pop ());
089                }
090        }
091
092
093
094        // is there a path between s and w?
095        public boolean hasPathTo(int w) {
096                return marked[w];
097        }
098
099        // return a path between s to w; null if no such path
100        public Iterable<Integer> pathTo(int w) {
101                if (!hasPathTo(w)) return null;
102                Stack<Integer> path = new Stack<>();
103                for (int x = w; x != s; x = edgeTo[x])
104                        path.push(x);
105                path.push(s);
106                return path;
107        }
108
109        public static void main(String[] args) {
110                args = new String [] { "data/tinyG.txt", "0" };
111                //args = new String [] { "data/tinyCG.txt", "0" };
112
113                In in = new In(args[0]);
114                Graph G = GraphGenerator.fromIn (in);
115                StdOut.println (G);
116                G.toGraphviz ("graph");
117
118                int s = Integer.parseInt(args[1]);
119                DepthFirstPaths dfs = new DepthFirstPaths(G, s);
120
121                for (int v = 0; v < G.V(); v++) {
122                        if (dfs.hasPathTo(v)) {
123                                StdOut.format("%d to %d:  ", s, v);
124                                for (int x : dfs.pathTo(v)) {
125                                        if (x == s) StdOut.print(x);
126                                        else        StdOut.print("-" + x);
127                                }
128                                StdOut.println();
129                        }
130
131                        else {
132                                StdOut.format("%d to %d:  not connected\n", s, v);
133                        }
134
135                }
136        }
137
138}