add DirectedDFS

README.md

@@ -61,6 +61,7 @@ Try to keep the interface and variable name consistent with the original book wh
   * [SymbolGraph](algs4/symbol_graph.py)
   * [DegreesOfSeparation](algs4/degrees_of_separation.py)
   * [Digraph](algs4/digraph.py)
+  * [DirectedDFS](algs4/directed_dfs.py)
 
 * 5 STRING
 

algs4/depth_first_search.py

@@ -34,7 +34,6 @@ def dfs(self, G, v):
 
 if __name__ == '__main__':
     import sys
-    print(sys.argv)
     f = open(sys.argv[1])
     s = int(sys.argv[2])
     V = int(f.readline())

algs4/directed_dfs.py

@@ -0,0 +1,56 @@
+"""
+    Execution:    python directed_dfs.py digraph.txt s
+    Data files:   https: // algs4.cs.princeton.edu / 42digraph / tinyDG.txt
+                  https://algs4.cs.princeton.edu/42digraph/mediumDG.txt
+                  https://algs4.cs.princeton.edu/42digraph/largeDG.txt
+
+    Determine single-source or multiple-source reachability in a digraph
+    using depth first search.
+    Runs in O(E + V) time.
+
+    % python directed_dfs.py tinyDG.txt 1
+    1
+
+    % python directed_dfs.py tinyDG.txt 2
+    0 1 2 3 4 5
+
+    % python directed_dfs.py tinyDG.txt 1 2 6
+    0 1 2 3 4 5 6 8 9 10 11 12 
+"""
+
+from algs4.digraph import Digraph
+
+
+class DirectedDFS:
+
+    def __init__(self, G, sources):
+        self._marked = [False for _ in range(G.V)]
+        for s in sources:
+            s = int(s)
+            if not self._marked[s]:
+                self.dfs(G, s)
+
+    def dfs(self, G, v):
+        self._marked[v] = True
+        for w in G.adj[v]:
+            if not self._marked[w]:
+                self.dfs(G, w)
+
+    def marked(self, v):
+        return self._marked[v]
+
+if __name__ == '__main__':
+    import sys
+    f = open(sys.argv[1])
+    V = int(f.readline())
+    E = int(f.readline())
+    g = Digraph(V)
+    for i in range(E):
+        v, w = f.readline().split()
+        g.add_edge(v, w)
+
+    reachable = DirectedDFS(g, sys.argv[2:])
+
+    for v in range(g.V):
+        if reachable.marked(v):
+            print(str(v) + " ")