Added algorithms for finding strong components and cycles.

Data/Graph/Inductive/Query.hs

@@ -3,6 +3,7 @@ module Data.Graph.Inductive.Query (module Q) where
 import Data.Graph.Inductive.Query.ArtPoint   as Q
 import Data.Graph.Inductive.Query.BCC        as Q
 import Data.Graph.Inductive.Query.BFS        as Q
+import Data.Graph.Inductive.Query.Cycles     as Q
 import Data.Graph.Inductive.Query.DFS        as Q
 import Data.Graph.Inductive.Query.Dominators as Q
 import Data.Graph.Inductive.Query.GVD        as Q
@@ -11,5 +12,6 @@ import Data.Graph.Inductive.Query.MaxFlow    as Q
 import Data.Graph.Inductive.Query.MaxFlow2   as Q
 import Data.Graph.Inductive.Query.Monad      as Q
 import Data.Graph.Inductive.Query.MST        as Q
+import Data.Graph.Inductive.Query.SCC        as Q
 import Data.Graph.Inductive.Query.SP         as Q
 import Data.Graph.Inductive.Query.TransClos  as Q

Data/Graph/Inductive/Query/Cycles.hs

@@ -0,0 +1,167 @@
+{- |
+   Module      : Data.Graph.Inductive.Query.Cycles
+   Description : Finds all cycles.
+   Copyright   : (c) Gabriel Hjort Blindell <[email protected]>
+                     Ivan Lazar Miljenovic <[email protected]>
+   License     : BSD3
+-}
+
+module Data.Graph.Inductive.Query.Cycles
+  ( cycles
+  , cycles'
+  , uniqueCycles
+  , uniqueCycles'
+  )
+where
+
+import Data.Graph.Inductive.Graph
+import Data.Graph.Inductive.Query.SCC
+
+import Data.List ((\\), delete, tails)
+import Data.Maybe (fromJust)
+import Control.Monad (ap)
+import qualified Data.IntMap as M
+
+
+
+-- The following functions were copied from the Graphalyze package.
+
+-- | Obtain the labels for a list of 'Node's. It is assumed that each 'Node' is
+-- indeed present in the given graph.
+addLabels :: (Graph g) => g a b -> [Node] -> [LNode a]
+addLabels gr = map (ap (,) (fromJust . lab gr))
+
+twoCycle      :: (Graph g) => g a b -> Node -> [Node]
+twoCycle gr n = filter (elem n . suc gr) (delete n $ suc gr n)
+
+-- | Determines if the list of nodes represents a regular subgraph.
+isRegular :: (Graph g) => g a b -> [Node] -> Bool
+isRegular g ns = all allTwoCycle split
+    where
+      -- Node + Rest of list
+      split = zip ns tns'
+      tns' = tail $ tails ns
+      allTwoCycle (n,rs) = null $ rs \\ twoCycle g n
+
+-- End of copied functions.
+
+
+
+-- | Contains the necessary data structures used by 'cycles'.
+data CyclesInState g a b
+  = CyclesInState
+      { cisCycles :: ![[Node]]
+        -- ^ The cycles found so far, in topological order.
+      , cisBlocked :: !(M.IntMap Bool)
+        -- ^ The nodes which are currently blocked.
+      , cisBlockMap :: !(M.IntMap [Node])
+        -- ^ The B set.
+      , cisStack :: ![Node]
+        -- ^ The node stack.
+      , cisComponents :: ![g a b]
+        -- ^ The components of the input graph.
+      , cisGraph :: !(g a b)
+        -- ^ The input graph.
+      }
+  deriving (Show, Read, Eq)
+
+-- | Finds all cycles in a given graph. The returned lists contains the nodes
+-- appearing in the cycles, in successor order (although it is undefined which
+-- node appears first).
+--
+-- Implemented using Johnson's algorithm. See Donald B. Johnson: Finding All the
+-- Elementary Circuits of a Directed Graph. SIAM Journal on Computing. Volumne
+-- 4, Nr. 1 (1975), pp. 77-84.
+cycles :: (Graph g) => g a b -> [[LNode a]]
+cycles g = map (addLabels g) (cycles' g)
+
+-- | Same as 'cycles' but does not return the node labels.
+cycles' :: (Graph g) => g a b -> [[Node]]
+cycles' g =
+  cisCycles $
+  foldr cyclesFor (mkInitCyclesInState g) (nodes g)
+
+-- | Find all cycles in the given graph (using 'cycles'), excluding those that
+-- are also cliques.
+uniqueCycles :: (Graph g) => g a b -> [[LNode a]]
+uniqueCycles g = map (addLabels g) (uniqueCycles' g)
+
+-- | Same as 'uniqueCycles' but does not return the node labels.
+uniqueCycles' :: (Graph g) => g a b -> [[Node]]
+uniqueCycles' g = filter (not . isRegular g) (cycles' g)
+
+cyclesFor :: (Graph g) => Node -> CyclesInState g a b -> CyclesInState g a b
+cyclesFor n st0 =
+  let n_comp = head $
+               filter (\c -> n `gelem` c) $
+               cisComponents st0
+  in if noNodes n_comp > 1
+     then let st1 = fst $ cCircuits n_comp n n st0
+              g = cisGraph st1
+              new_g = delNode n g
+              new_comps = strongComponentsOf new_g
+              st2 = st1 { cisGraph = new_g
+                        , cisComponents = new_comps
+                        }
+          in st2
+     else st0 -- Skip to next node
+
+cCircuits :: (Graph g) => (g a b) -> Node -> Node -> CyclesInState g a b ->
+             (CyclesInState g a b, Bool)
+cCircuits c s n st0 =
+  let st1 = st0 { cisBlocked = M.insert n True (cisBlocked st0)
+                , cisStack = (n:cisStack st0)
+                }
+      n_suc = suc c n
+      (st2, f) = foldr (cCircuitsVisit c s) (st1, False) n_suc
+      st3 = if f
+            then cUnblock n st2
+            else foldr (cCircuitsBlock n) st2 n_suc
+      st4 = st3 { cisStack = tail $ cisStack st3 }
+  in (st4, f)
+
+cCircuitsVisit :: (Graph g) => (g a b) -> Node -> Node ->
+                  (CyclesInState g a b, Bool) -> (CyclesInState g a b, Bool)
+cCircuitsVisit c s n (st0, f0)
+  | n == s =
+      let new_cycle = reverse $ cisStack st0
+          st1 = st0 { cisCycles = (new_cycle:cisCycles st0) }
+      in (st1, True)
+  | not (cisBlocked st0 M.! n) =
+      let (st1, f1) = cCircuits c s n st0
+      in (st1, f0 || f1)
+  | otherwise = (st0, f0)
+
+cCircuitsBlock :: (Graph g) => Node -> Node -> CyclesInState g a b ->
+                  CyclesInState g a b
+cCircuitsBlock n m st0 =
+  let bm = cisBlockMap st0
+      m_blocked = bm M.! m
+      new_m_blocked = (n:m_blocked)
+  in if n `notElem` m_blocked
+     then st0 { cisBlockMap = M.insert m new_m_blocked bm }
+     else st0
+
+cUnblock :: (Graph g) => Node -> CyclesInState g a b -> CyclesInState g a b
+cUnblock n st0 =
+  let n_blocked = cisBlockMap st0 M.! n
+      st1 = st0 { cisBlocked = M.insert n False (cisBlocked st0)
+                , cisBlockMap = M.insert n [] (cisBlockMap st0)
+                }
+      st2 = foldr ( \m st ->
+                    if cisBlocked st M.! m then cUnblock m st else st
+                  )
+                  st1
+                  n_blocked
+  in st2
+
+mkInitCyclesInState :: (Graph g) => g a b -> CyclesInState g a b
+mkInitCyclesInState g =
+  let ns = nodes g
+  in CyclesInState { cisCycles = []
+                   , cisBlocked = M.fromList $ zip ns (repeat False)
+                   , cisBlockMap = M.fromList $ zip ns (repeat [])
+                   , cisStack = []
+                   , cisComponents = strongComponentsOf g
+                   , cisGraph = g
+                   }

Data/Graph/Inductive/Query/SCC.hs

@@ -0,0 +1,128 @@
+{- |
+   Module      : Data.Graph.Inductive.Query.SCC
+   Description : Finds all strongly connected components.
+   Copyright   : (c) Gabriel Hjort Blindell <[email protected]>
+   License     : BSD3
+-}
+
+module Data.Graph.Inductive.Query.SCC
+  ( strongComponentsOf )
+where
+
+import Data.Graph.Inductive.Graph
+
+import qualified Data.IntMap as M
+
+
+
+-- | Node information (whether the node is on the stack, its index, and its low
+-- link), which is used as part of 'SCCState'.
+data SCCNodeInfo
+  = SCCNodeInfo
+      { sccIsNodeOnStack :: Bool
+      , sccNodeIndex :: Int
+      , sccNodeLowLink :: Int
+      }
+  deriving (Show, Read, Eq)
+
+-- | Contains the necessary data structures used by 'strongComponentsOf'.
+data SCCState g a b
+  = SCCState
+      { sccComponents :: !([g a b])
+        -- ^ The components found so far.
+      , sccCurrentIndex :: !Int
+        -- ^ The current index.
+      , sccStack :: ![Node]
+        -- ^ The node stack.
+      , sccNodeInfo :: !(M.IntMap SCCNodeInfo)
+        -- ^ Node information.
+      , sccGraph :: !(g a b)
+        -- ^ The input graph.
+      }
+  deriving (Show, Read, Eq)
+
+-- | Find all strongly connected components of a graph. Returned list is sorted
+-- in topological order.
+--
+-- Implements Tarjan's algorithm:
+-- https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm
+strongComponentsOf :: (Graph g) => g a b -> [g a b]
+strongComponentsOf g =
+  sccComponents $
+  foldr ( \n st ->
+          let i = sccNodeIndex $ sccNodeInfo st M.! n
+          in if i < 0 then findSCCFor n st else st
+        )
+        (mkInitSCCState g)
+        (nodes g)
+
+findSCCFor :: (Graph g) => Node -> SCCState g a b -> SCCState g a b
+findSCCFor n st0 =
+  let i = sccCurrentIndex st0
+      st1 = st0 { sccCurrentIndex = i + 1
+                , sccStack = (n:sccStack st0)
+                , sccNodeInfo = M.insert n
+                                         (SCCNodeInfo True i i)
+                                         (sccNodeInfo st0)
+                }
+      g = sccGraph st1
+      st2 = foldr computeLowLinks st1 (suc g n)
+      ni = sccNodeInfo st2 M.! n
+      index = sccNodeIndex ni
+      lowlink = sccNodeLowLink ni
+      st3 = if index == lowlink then produceSCC st2 else st2
+  in st3
+  where
+    computeLowLinks m st
+      | isIndexUndefined =
+          let st' = findSCCFor m st
+              ni = sccNodeInfo st' M.! n
+              n_lowlink = sccNodeLowLink ni
+              m_lowlink = sccNodeLowLink $ sccNodeInfo st' M.! m
+              new_ni = ni { sccNodeLowLink = min n_lowlink m_lowlink }
+          in st' { sccNodeInfo = M.insert n new_ni (sccNodeInfo st') }
+      | isOnStack =
+          let ni = sccNodeInfo st M.! n
+              n_lowlink = sccNodeLowLink ni
+              m_index = sccNodeIndex $ sccNodeInfo st M.! m
+              new_ni = ni { sccNodeLowLink = min n_lowlink m_index }
+          in st { sccNodeInfo = M.insert n new_ni (sccNodeInfo st) }
+      | otherwise = st
+      where isIndexUndefined = let i = sccNodeIndex $ (sccNodeInfo st) M.! m
+                               in i < 0
+            isOnStack = sccIsNodeOnStack $ (sccNodeInfo st) M.! m
+    produceSCC st =
+      let stack = sccStack st
+          (p0, p1) = span (/= n) stack
+          ns = (head p1:p0)
+          lab_ns = filter (\(n', _) -> n' `elem` ns) $
+                   labNodes $
+                   sccGraph st
+          new_stack = tail p1
+          new_map = foldr ( \n' ni_map ->
+                            let ni = ni_map M.! n'
+                                new_ni = ni { sccIsNodeOnStack = False }
+                            in M.insert n' new_ni ni_map
+                          )
+                          (sccNodeInfo st)
+                          ns
+          lab_es = filter (\(n', m', _) -> n' `elem` ns && m' `elem` ns) $
+                   labEdges $
+                   sccGraph st
+          comp = mkGraph lab_ns lab_es
+          new_cs = (comp:sccComponents st)
+      in st { sccComponents = new_cs
+            , sccStack = new_stack
+            , sccNodeInfo = new_map
+            }
+
+mkInitSCCState :: (Graph g) => g a b -> SCCState g a b
+mkInitSCCState g =
+  let ns = nodes g
+      init_ni = SCCNodeInfo False (-1) (-1)
+  in SCCState { sccComponents = []
+              , sccCurrentIndex = 0
+              , sccStack = []
+              , sccNodeInfo = M.fromList $ zip ns (repeat init_ni)
+              , sccGraph = g
+              }

Data/Graph/Inductive/Query/SP.hs

@@ -63,7 +63,7 @@ spLength s t = getDistance t . spTree s
 
 -- | Shortest path between two nodes, if any.
 --
---   Returns 'Nothing' if the destination is not reachable from teh
+--   Returns 'Nothing' if the destination is not reachable from the
 --   start node, and @'Just' <path>@ otherwise.
 --
 --   The edge labels of type @b@ are the edge weights; negative edge

fgl.cabal

@@ -50,6 +50,7 @@ library {
         Data.Graph.Inductive.Query.ArtPoint,
         Data.Graph.Inductive.Query.BCC,
         Data.Graph.Inductive.Query.BFS,
+        Data.Graph.Inductive.Query.Cycles,
         Data.Graph.Inductive.Query.DFS,
         Data.Graph.Inductive.Query.Dominators,
         Data.Graph.Inductive.Query.GVD,
@@ -58,6 +59,7 @@ library {
         Data.Graph.Inductive.Query.MaxFlow,
         Data.Graph.Inductive.Query.MaxFlow2,
         Data.Graph.Inductive.Query.Monad,
+        Data.Graph.Inductive.Query.SCC,
         Data.Graph.Inductive.Query.SP,
         Data.Graph.Inductive.Query.TransClos,
         Data.Graph.Inductive