least reachable city

03_dijkstra/LeastReachableCity.hs

@@ -1,15 +1,25 @@
-module LeastReachableCity  where
+module LeastReachableCity(dijkstra, leastReachableCity) where
 
 import Types 
 import qualified Data.Map as Map
 import qualified Data.Set as Set
 
+-- Well, it's just a magic number, because it's too much hassle to implement type like "Len val | Infinity" 
+-- TODO: get graph radius and use this number as infinity
 infinity :: Len
 infinity = 999999 :: Len
 
+leastReachableCity :: Graph -> Len -> (Point, Int)
+leastReachableCity graph mileage = foldl (\(p, n) (p', n') -> 
+        if n' < n then (p',n') 
+        else (p, n)) 
+    (-1, infinity) [(city, countReachableCities $ dijkstra city graph) | city <- Set.toList $ fst $ countVertices graph] where
+        countReachableCities :: Distances -> Int
+        countReachableCities distances = Map.foldl (\n val -> if (val <= mileage) && (val /= 0) then n + 1 else n) 0 distances 
+
 dijkstra :: Point -> Graph -> Distances
 dijkstra start graph = dijkstra' start graph visited_init to_visit_init distances_init where
-    -- Helper
+    -- Helper (so we don' need to call dijkstra initializing empty visited, to_visit etc)
     dijkstra' :: Point -> Graph -> Vertices -> Vertices -> Distances -> Distances 
     dijkstra' start graph visited to_visit distances = if Set.null to_visit 
         then 
@@ -22,9 +32,9 @@ dijkstra start graph = dijkstra' start graph visited_init to_visit_init distance
                 (Set.union (Set.delete start to_visit) $ findNotVisitedNeighbours graph visited start) 
                 (updateDistances graph start distances)
     -- Other
-    to_visit_init = (Set.insert start $ Set.empty :: Set.Set Point)
+    to_visit_init = (Set.insert start $ Set.empty :: Vertices)
-    distances_init = (infinityDistances start $ countVertices graph)
+    distances_init = (infinityDistances start $ snd $ countVertices graph)
-    visited_init = (Set.empty :: Set.Set Point) 
+    visited_init = (Set.empty :: Vertices) 
 
 updateDistances :: Graph -> Point -> Distances -> Distances
 updateDistances graph point distances = snd $ Map.foldrWithKey decideMin ((point, Map.findWithDefault (-1) point distances), Map.empty :: Distances) distances where
@@ -42,13 +52,13 @@ findMinNotVisited to_visit distances = fst $ Set.foldl (\(p, l) p' -> case Map.l
     (Just l') -> if l' < l then 
             (p', l') 
         else (p,l)) 
-    (-1, maxBound) to_visit 
+    (-1, infinity) to_visit 
 
 infinityDistances :: Point -> Int -> Distances
 infinityDistances point n = Map.fromList $ (point, 0) : [(x, infinity) | x <- [1..n], x /= point] 
 
-countVertices :: Graph -> Int
+countVertices :: Graph -> (Vertices, Int)
-countVertices graph = snd $ foldl f (Set.empty :: Set.Set Point, 0) graph where
+countVertices graph = foldl f (Set.empty :: Vertices, 0) graph where
     f :: (Vertices, Int) -> Node -> (Vertices, Int)
     f (vertices, n) (Node (a, b, _)) = 
         let aIsNotMember = not $ Set.member a vertices 

03_dijkstra/data

@@ -0,0 +1,9 @@
+4
+
+1 2 10
+1 4 2
+1 3 3
+3 2 5
+2 4 6
+4 5 4
+5 3 1

03_dijkstra/main.hs

@@ -2,7 +2,7 @@ module Main where
 
 import System.IO 
 import System.Environment
-import System.Directory
+
 import qualified Data.Map as Map
 import qualified Data.Set as Set
 
@@ -21,21 +21,16 @@ main = do
     argv <- getArgs
 
     filename <- if not $ null argv then do
-        putStrLn $ "Trying to read file " ++ "\"" ++ head argv ++ "\""
         head <$> getArgs
     else do
-        error "Not enough arguments,\nusage: main [filename]"
+        putStrLn "Usage: ./lrc [filename]\nNow defaulting to file \"data\""
+        return "data"
 
     content <- readFile filename
     let mileage = read $ head $ lines content :: Len
-    
     let graph = readGraph $ tail content
-    --let dist = findNeighbours 1 graph
+    let (city, n) = leastReachableCity graph mileage
-    --print $ findNotVisitedNeighbours graph (Set.fromList [1,3]) 2
+    putStrLn $ "The least reachable city is " ++ (show city) ++ " (" ++ (show n) ++ " city/ies is/are reachable)"
-    print $ dijkstra 1 graph 
-    --print $ updateDistances graph 2 (Map.fromList [(1, 100), (2, 1), (3, 200)])  
-    --print $ infinityDistances 1 4
-    --print $ findMinNotVisited (Set.fromList [1, 2, 3] :: Set.Set Int) (Map.fromList [(1, 123), (2, 114), (3, 115)]) 
 
 {- For parsing graph using content of the file -} 
 parseStrNode :: [String] -> Node