From ee6e59f9d9c94b3a11667e4efb5d3b634bf8cf6e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Eray=20=C3=96zkural?= <eray@pardus.org.tr>
Date: Mon, 18 Jul 2005 13:11:39 +0000
Subject: [PATCH] * cycle var mi bakan code yaz. testini de yap. testisini de.

---
 pisi/graph.py       | 20 ++++++++++++++++----
 tests/graphtests.py | 12 ++++++------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/pisi/graph.py b/pisi/graph.py
index e0befeaf..e0dd636f 100644
--- a/pisi/graph.py
+++ b/pisi/graph.py
@@ -1,5 +1,8 @@
 # the most simple minded digraph class ever
 
+class CycleError:
+    pass
+
 class digraph(object):
 
     def __init__(self):
@@ -66,7 +69,7 @@ class digraph(object):
         self.d = {}
         self.f = {}
         for u in self.__v:
-            self.color[u] = 'w'
+            self.color[u] = 'w'         # mark white (unexplored)
             self.p[u] = None
         self.time = 0
         for u in self.__v:
@@ -74,17 +77,26 @@ class digraph(object):
                 self.dfs_visit(u, finish_hook)
 
     def dfs_visit(self, u, finish_hook):
-        self.color[u] = 'g'
+        self.color[u] = 'g'             # mark green (discovered)
         self.d[u] = self.time = self.time + 1
         for v in self.adj(u):
-            if self.color[v] == 'w':
+            if self.color[v] == 'w':    # explore unexplored vertices
                 self.p[v] = u
                 self.dfs_visit(v, finish_hook)
-        self.color[u] = 'b'
+            elif self.color[v] == 'g':  # cycle detected
+                raise CycleError
+        self.color[u] = 'b'             # mark black (completed)
         if finish_hook:
             finish_hook(u)
         self.f[u] = self.time = self.time + 1
 
+    def cycle_free(self):
+        try:
+            self.dfs()
+            return True
+        except CycleError:
+            return False
+
     def topological_sort(self):
         l = []
         self.dfs(lambda u: l.append(u))
diff --git a/tests/graphtests.py b/tests/graphtests.py
index 469e5b3d..826e7085 100644
--- a/tests/graphtests.py
+++ b/tests/graphtests.py
@@ -7,15 +7,15 @@ from pisi.config import config
 
 class GraphTestCase(unittest.TestCase):
     def setUp(self):
-        g0 = graph.digraph()
-        g0.from_list([ (1,2), (1,3), (2,3), (3,4), (4, 5), (4,1)])
+        self.g0 = graph.digraph()
+        self.g0.from_list([ (1,2), (1,3), (2,3), (3,4), (4, 5), (4,1)])
         
-        g1 = graph.digraph()
-        g1.from_list([ (0,2), (0,3), (3,4), (2,4), (0,5), (5,4) ])
-        self.g1 = g1
+        self.g1 = graph.digraph()
+        self.g1.from_list([ (0,2), (0,3), (3,4), (2,4), (0,5), (5,4) ])
 
     def testCycle(self):
-        pass
+        self.assert_(not self.g0.cycle_free())
+        self.assert_(self.g1.cycle_free())
 
     def testTopologicalSort(self):
         order = self.g1.topological_sort()