add digraph

README.md

@@ -60,10 +60,12 @@ Try to keep the interface and variable name consistent with the original book wh
   * [Cycle](algs4/cycle.py)
   * [SymbolGraph](algs4/symbol_graph.py)
   * [DegreesOfSeparation](algs4/degrees_of_separation.py)
+  * [Digraph](algs4/digraph.py)
 
 * 5 STRING
 
   * [LSD](algs4/lsd.py)
+
 ## License
 
 This code is released under MIT.

algs4/digraph.py

@@ -0,0 +1,85 @@
+"""
+   Execution:    python digraph.py input.txt
+   Dependencies: Bag.java Stack.java In.java StdOut.java
+   Data files:   https://algs4.cs.princeton.edu/41graph/tinyDG.txt
+                 https://algs4.cs.princeton.edu/41graph/mediumDG.txt
+                 https://algs4.cs.princeton.edu/41graph/largeDG.txt
+ 
+   A graph, implemented using an array of sets.
+   Parallel edges and self-loops are permitted.
+ 
+   % python digraph.py < tinyDG.txt
+   13 vertices, 22 edges
+   0: 5 1 
+   1: 
+   2: 0 3 
+   3: 5 2 
+   4: 3 2 
+   5: 4 
+   6: 9 4 8 0 
+   7: 6 9
+   8: 6 
+   9: 11 10 
+   10: 12 
+   11: 4 12 
+   12: 9 
+ 
+ """
+
+
+class Digraph:
+
+    def __init__(self, v):
+        self.V = v
+        self.E = 0
+        self.adj = {}
+        for v in range(self.V):
+            self.adj[v] = []
+
+    def __str__(self):
+        s = "%d vertices, %d edges\n" % (self.V, self.E)
+        s += "\n".join("%d: %s" % (v, " ".join(str(w)
+                                               for w in self.adj[v])) for v in range(self.V))
+        return s
+
+    def add_edge(self, v, w):
+        v, w = int(v), int(w)
+        self.adj[v].append(w)
+        self.E += 1
+
+    def degree(self, v):
+        return len(self.adj[v])
+
+    def max_degree(self):
+        max_deg = 0
+        for v in self.V:
+            max_deg = max(max_deg, self.degree(v))
+        return max_deg
+
+    def number_of_self_loops(self):
+        count = 0
+        for v in range(self.V):
+            for w in self.adj[v]:
+                if w == v:
+                    count += 1
+        return count
+
+    def reverse(self):
+        R = Digraph(self.V)
+        v = 0
+        while v < self.V:
+            for w in self.adj[v]:
+                R.add_edge(w, v)
+            v += 1
+        return R
+
+if __name__ == '__main__':
+    import sys
+
+    V = int(sys.stdin.readline())
+    E = int(sys.stdin.readline())
+    g = Digraph(V)
+    for i in range(E):
+        v, w = sys.stdin.readline().split()
+        g.add_edge(v, w)
+    print(g)

algs4/graph.py

@@ -63,9 +63,6 @@ def max_degree(self):
             max_deg = max(max_deg, self.degree(v))
         return max_deg
 
-    def avg_degree(self):
-        return 2 * self.E / self.V
-
     def number_of_self_loops(self):
         count = 0
         for v in range(self.V):