add depth_first_order

README.md

@@ -51,18 +51,22 @@ Try to keep the interface and variable name consistent with the original book wh
   * [LinearProbingHashST](algs4/linear_probing_hash_st.py)
 
 * 4 GRAPHS
-
-  * [Graph](algs4/graph.py)
-  * [DepthFirstSearch](algs4/depth_first_search.py)
-  * [DepthFirstPaths](algs4/depth_first_paths.py)
-  * [BreadthFirstPaths](algs4/breadth_first_paths.py)
-  * [CC](algs4/cc.py)
-  * [Cycle](algs4/cycle.py)
-  * [SymbolGraph](algs4/symbol_graph.py)
-  * [DegreesOfSeparation](algs4/degrees_of_separation.py)
-  * [Digraph](algs4/digraph.py)
-  * [DirectedDFS](algs4/directed_dfs.py)
-  * [DirectedCycle](algs4/directed_cycle.py)
+  * Graph
+    * [Graph](algs4/graph.py)
+    * [DepthFirstSearch](algs4/depth_first_search.py)
+    * [DepthFirstPaths](algs4/depth_first_paths.py)
+    * [BreadthFirstPaths](algs4/breadth_first_paths.py)
+    * [CC](algs4/cc.py)
+    * [Cycle](algs4/cycle.py)
+    * [SymbolGraph](algs4/symbol_graph.py)
+    * [DegreesOfSeparation](algs4/degrees_of_separation.py)
+  * Digraph
+    * [Digraph](algs4/digraph.py)
+    * [DirectedDFS](algs4/directed_dfs.py)
+    * [DirectedCycle](algs4/directed_cycle.py)
+    * [DepthFirstOrder](depth_first_order.go)
+    * [Topological](topological.go)
+    * [KosarajuSCC](kosaraju_scc.go)
 
 * 5 STRING
 

algs4/depth_first_order.py

@@ -0,0 +1,79 @@
+"""
+ *  Execution:    python depth_first_order.py digraph.txt
+ *  Data files:   https://algs4.cs.princeton.edu/42digraph/tinyDAG.txt
+ *                https://algs4.cs.princeton.edu/42digraph/tinyDG.txt
+ *
+ *  Compute preorder and postorder for a digraph or edge-weighted digraph.
+ *  Runs in O(E + V) time.
+ *
+ *  % python depth_first_order.py tinyDAG.txt
+ *     v  pre post
+ *  --------------
+ *     0    0    8
+ *     1    3    2
+ *     2    9   10
+ *     3   10    9
+ *     4    2    0
+ *     5    1    1
+ *     6    4    7
+ *     7   11   11
+ *     8   12   12
+ *     9    5    6
+ *    10    8    5
+ *    11    6    4
+ *    12    7    3
+ *  Preorder:  0 5 4 1 6 9 11 12 10 2 3 7 8
+ *  Postorder: 4 5 1 12 11 10 9 6 0 3 2 7 8
+ *  Reverse postorder: 8 7 2 3 0 6 9 10 11 12 1 5 4
+ *
+"""
+from algs4.queue import Queue
+from algs4.stack import Stack
+from algs4.digraph import Digraph
+
+
+class DepthFirstOrder:
+
+    def __init__(self, G):
+        self.marked = [False for _ in range(G.V)]
+        self.pre = Queue()
+        self.post = Queue()
+        for w in range(G.V):
+            if not self.marked[w]:
+                self.dfs(g, w)
+
+    def dfs(self, G, v):
+        self.pre.enqueue(v)
+        self.marked[v] = True
+
+        for w in G.adj[v]:
+            if not self.marked[w]:
+                self.dfs(G, w)
+        self.post.enqueue(v)
+
+    def reversePost(self):
+        reverse = Stack()
+        for v in self.post:
+            reverse.push(v)
+        return reverse
+
+
+if __name__ == '__main__':
+    import sys
+    g = Digraph(file=open(sys.argv[1]))
+    dfs = DepthFirstOrder(g)
+
+    print("Preorder: ")
+    for v in dfs.pre:
+        print(v, " ", end="")
+    print()
+
+    print("Postorder: ")
+    for v in dfs.post:
+        print(v, " ", end="")
+    print()
+
+    print("ReversePostorder: ")
+    for v in dfs.reversePost():
+        print(v, " ", end="")
+    print()

algs4/digraph.py

@@ -25,16 +25,28 @@
    12: 9 
  
  """
+from algs4.bag import Bag
 
 
 class Digraph:
 
-    def __init__(self, v):
+    def __init__(self, v=0, **kwargs):
         self.V = v
         self.E = 0
         self.adj = {}
         for v in range(self.V):
-            self.adj[v] = []
+            self.adj[v] = Bag()
+
+        if 'file' in kwargs:
+            # init a digraph by a file input
+            in_file = kwargs['file']
+            self.V = int(in_file.readline())
+            for v in range(self.V):
+                self.adj[v] = Bag()
+            E = int(in_file.readline())
+            for i in range(E):
+                v, w = in_file.readline().split()
+                self.add_edge(int(v), int(w))
 
     def __str__(self):
         s = "%d vertices, %d edges\n" % (self.V, self.E)
@@ -44,7 +56,7 @@ def __str__(self):
 
     def add_edge(self, v, w):
         v, w = int(v), int(w)
-        self.adj[v].append(w)
+        self.adj[v].add(w)
         self.E += 1
 
     def degree(self, v):
@@ -73,6 +85,7 @@ def reverse(self):
             v += 1
         return R
 
+
 if __name__ == '__main__':
     import sys
 

algs4/graph.py

@@ -31,6 +31,7 @@
    2: 141 110 108 86 79 51 42 18 14 
    ...
  """
+from algs4.bag import Bag
 
 
 class Graph:
@@ -40,7 +41,7 @@ def __init__(self, v):
         self.E = 0
         self.adj = {}
         for v in range(self.V):
-            self.adj[v] = []
+            self.adj[v] = Bag()
 
     def __str__(self):
         s = "%d vertices, %d edges\n" % (self.V, self.E)
@@ -50,8 +51,8 @@ def __str__(self):
 
     def add_edge(self, v, w):
         v, w = int(v), int(w)
-        self.adj[v].append(w)
-        self.adj[w].append(v)
+        self.adj[v].add(w)
+        self.adj[w].add(v)
         self.E += 1
 
     def degree(self, v):
@@ -71,6 +72,7 @@ def number_of_self_loops(self):
                     count += 1
         return count
 
+
 if __name__ == '__main__':
     import sys