Data.Graph

O((V+E) \log V). Build a graph from a list of nodes uniquely identified by keys, with a list of keys of nodes this node should have edges to.

This function takes an adjacency list representing a graph with vertices of type key labeled by values of type node and produces a Graph-based representation of that list. The Graph result represents the shape of the graph, and the functions describe a) how to retrieve the label and adjacent vertices of a given vertex, and b) how to retrieve a vertex given a key.

(graph, nodeFromVertex, vertexFromKey) = graphFromEdges edgeList

• graph :: Graph is the raw, array based adjacency list for the graph.

• nodeFromVertex :: Vertex -> (node, key, [key]) returns the node associated with the given 0-based Int vertex; see warning below. This runs in O(1) time.

• vertexFromKey :: key -> Maybe Vertex returns the Int vertex for the key if it exists in the graph, Nothing otherwise. This runs in O(\log V) time.

To safely use this API you must either extract the list of vertices directly from the graph or first call vertexFromKey k to check if a vertex corresponds to the key k. Once it is known that a vertex exists you can use nodeFromVertex to access the labelled node and adjacent vertices. See below for examples.

Note: The out-list may contain keys that don't correspond to nodes of the graph; they are ignored.

Warning: The nodeFromVertex function will cause a runtime exception if the given Vertex does not exist.

Examples

An empty graph.

(graph, nodeFromVertex, vertexFromKey) = graphFromEdges []
graph = array (0,-1) []

A graph where the out-list references unspecified nodes ('c'), these are ignored.

(graph, _, _) = graphFromEdges [("a", 'a', ['b']), ("b", 'b', ['c'])]
array (0,1) [(0,[1]),(1,[])]

A graph with 3 vertices: ("a") -> ("b") -> ("c")

(graph, nodeFromVertex, vertexFromKey) = graphFromEdges [("a", 'a', ['b']), ("b", 'b', ['c']), ("c", 'c', [])]
graph == array (0,2) [(0,[1]),(1,[2]),(2,[])]
nodeFromVertex 0 == ("a",'a',"b")
vertexFromKey 'a' == Just 0

Get the label for a given key.

let getNodePart (n, _, _) = n
(graph, nodeFromVertex, vertexFromKey) = graphFromEdges [("a", 'a', ['b']), ("b", 'b', ['c']), ("c", 'c', [])]
getNodePart . nodeFromVertex <$> vertexFromKey 'a' == Just "A"

O((V+E) \log V). Identical to graphFromEdges, except that the return value does not include the function which maps keys to vertices. This version of graphFromEdges is for backwards compatibility.

O(V+E). Build a graph from a list of edges.

Warning: This function will cause a runtime exception if a vertex in the edge list is not within the given Bounds.

Examples

buildG (0,-1) [] == array (0,-1) []
buildG (0,2) [(0,1), (1,2)] == array (0,1) [(0,[1]),(1,[2])]
buildG (0,2) [(0,1), (0,2), (1,2)] == array (0,2) [(0,[2,1]),(1,[2]),(2,[])]

O(V). Returns the list of vertices in the graph.

Examples

vertices (buildG (0,-1) []) == []

vertices (buildG (0,2) [(0,1),(1,2)]) == [0,1,2]

O(V+E). Returns the list of edges in the graph.

Examples

edges (buildG (0,-1) []) == []

edges (buildG (0,2) [(0,1),(1,2)]) == [(0,1),(1,2)]

O(V+E). A table of the count of edges from each node.

Examples

outdegree (buildG (0,-1) []) == array (0,-1) []

outdegree (buildG (0,2) [(0,1), (1,2)]) == array (0,2) [(0,1),(1,1),(2,0)]

O(V+E). A table of the count of edges into each node.

Examples

indegree (buildG (0,-1) []) == array (0,-1) []

indegree (buildG (0,2) [(0,1), (1,2)]) == array (0,2) [(0,0),(1,1),(2,1)]

O(V+E). The graph obtained by reversing all edges.

Examples

transposeG (buildG (0,2) [(0,1), (1,2)]) == array (0,2) [(0,[]),(1,[0]),(2,[1])]

O(V+E). A spanning forest of the part of the graph reachable from the listed vertices, obtained from a depth-first search of the graph starting at each of the listed vertices in order.

O(V+E). A spanning forest of the graph, obtained from a depth-first search of the graph starting from each vertex in an unspecified order.

O(V+E). A topological sort of the graph. The order is partially specified by the condition that a vertex i precedes j whenever j is reachable from i but not vice versa.

Note: A topological sort exists only when there are no cycles in the graph. If the graph has cycles, the output of this function will not be a topological sort. In such a case consider using scc.

O(V+E). Reverse ordering of topSort.

See note in topSort.

O(V+E). The connected components of a graph. Two vertices are connected if there is a path between them, traversing edges in either direction.

O(V+E). The strongly connected components of a graph, in reverse topological order.

Examples

scc (buildG (0,3) [(3,1),(1,2),(2,0),(0,1)])
  == [Node {rootLabel = 0, subForest = [Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []}]}]}
     ,Node {rootLabel = 3, subForest = []}]

O(V+E). The biconnected components of a graph. An undirected graph is biconnected if the deletion of any vertex leaves it connected.

The input graph is expected to be undirected, i.e. for every edge in the graph the reverse edge is also in the graph. If the graph is not undirected the output is arbitrary.

O(V+E). Returns the list of vertices reachable from a given vertex.

Examples

reachable (buildG (0,0) []) 0 == [0]

reachable (buildG (0,2) [(0,1), (1,2)]) 0 == [0,1,2]

O(V+E). Returns True if the second vertex reachable from the first.

Examples

path (buildG (0,0) []) 0 0 == True

path (buildG (0,2) [(0,1), (1,2)]) 0 2 == True

path (buildG (0,2) [(0,1), (1,2)]) 2 0 == False

O((V+E) \log V). The strongly connected components of a directed graph, reverse topologically sorted.

Examples

stronglyConnComp [("a",0,[1]),("b",1,[2,3]),("c",2,[1]),("d",3,[3])]
  == [CyclicSCC ["d"],CyclicSCC ["b","c"],AcyclicSCC "a"]

O((V+E) \log V). The strongly connected components of a directed graph, reverse topologically sorted. The function is the same as stronglyConnComp, except that all the information about each node retained. This interface is used when you expect to apply SCC to (some of) the result of SCC, so you don't want to lose the dependency information.

Examples

stronglyConnCompR [("a",0,[1]),("b",1,[2,3]),("c",2,[1]),("d",3,[3])]
 == [CyclicSCC [("d",3,[3])],CyclicSCC [("b",1,[2,3]),("c",2,[1])],AcyclicSCC ("a",0,[1])]

The vertices of a strongly connected component.

The vertices of a list of strongly connected components.