Initial fork commit

scripts/geodata/graph/scc.py

@@ -0,0 +1,41 @@
+VISIT, VISIT_EDGE, POST_VISIT = range(3)
+
+
+def strongly_connected_components(graph):
+    '''
+    Find strongly connected components in a graph using iterative
+    depth-first search.
+
+    Based on:
+    http://code.activestate.com/recipes/578507-strongly-connected-components-of-a-directed-graph/
+    '''
+    identified = set()
+    stack = []
+    index = {}
+    boundaries = []
+
+    for v in graph:
+        if v not in index:
+            todo = [(VISIT, v)]
+            while todo:
+                op, v = todo.pop()
+                if op == VISIT:
+                    index[v] = len(stack)
+                    stack.append(v)
+                    boundaries.append(index[v])
+                    todo.append((POST_VISIT, v))
+                    todo.extend([(VISIT_EDGE, w) for w in graph[v]])
+                elif op == VISIT_EDGE:
+                    if v not in index:
+                        todo.append((VISIT, v))
+                    elif v not in identified:
+                        while index[v] < boundaries[-1]:
+                            boundaries.pop()
+                else:
+                    # op == POST_VISIT
+                    if boundaries[-1] == index[v]:
+                        boundaries.pop()
+                        scc = stack[index[v]:]
+                        del stack[index[v]:]
+                        identified.update(scc)
+                        yield scc

scripts/geodata/graph/topsort.py

@@ -0,0 +1,32 @@
+
+def topsort(graph):
+    '''
+    Topological sort for a dependency graph, e.g.
+
+    Usage:
+
+    >>> graph = {
+            'a': ['b'],
+            'b': ['d'],
+            'c': ['d', 'a'],
+            'd': [],
+        }
+    >>> topsort(graph)
+
+    Returns: ['d', 'b', 'a', 'c']
+
+    '''
+    todos = set(graph.keys())
+    seen = set()
+    result = []
+    while todos:
+        for key in todos:
+            deps = graph[key]
+            if len([d for d in deps if d in seen]) == len(deps):
+                break
+        else:
+            raise Exception('Cycle: {}'.format(todos))
+        todos.remove(key)
+        result.append(key)
+        seen.add(key)
+    return result