From d5a7f778f9fb81c9ed3e339de80d31c68f45c9fc Mon Sep 17 00:00:00 2001
From: Abhinav Sarkar <abhinav.sarkar@gmail.com>
Date: Tue, 23 Oct 2012 22:20:04 +0530
Subject: [PATCH] More performance enhancements in SudokuSolver

---
 .gitignore      |  1 +
 SudokuSolver.hs | 77 +++++++++++++++++++++++++++++++------------------
 rubyquiz.cabal  |  2 +-
 3 files changed, 51 insertions(+), 29 deletions(-)

diff --git a/.gitignore b/.gitignore
index c67f7ef..7147a98 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 *.hi
 *.o
 *.bak
+*.prof
 input
 bin
 dist
diff --git a/SudokuSolver.hs b/SudokuSolver.hs
index 375a49e..49137cc 100644
--- a/SudokuSolver.hs
+++ b/SudokuSolver.hs
@@ -2,10 +2,10 @@
 
 module Main where
 
-import qualified Data.Map as M
 import qualified Data.Set as S
-import Control.Concurrent (forkIO)
-import Control.Monad (foldM, forM_)
+import qualified Data.HashMap.Strict as M
+import Control.Concurrent (forkIO, newEmptyMVar, putMVar, takeMVar)
+import Control.Monad (foldM, forM_, forM)
 import Data.Char (digitToInt, intToDigit)
 import Data.List (foldl', intersperse, intercalate, (\\))
 import Data.List.Split (chunksOf)
@@ -16,19 +16,23 @@ import Text.Printf (printf)
 data Cell = Cell {-# UNPACK #-} !Int
                  ![Int]
                  {-# UNPACK #-} !Int
-                 deriving (Eq)
 
-data Board = Board { ixMap :: !(M.Map Int Cell),
+data Board = Board { ixMap :: !(M.HashMap Int Cell),
                      ambCells :: !(S.Set Cell)
-                   } deriving (Eq, Ord, Show)
+                   } deriving (Eq, Show)
+
+instance Eq Cell where
+  {-# INLINE (==) #-}
+  (Cell i1 v1 _) == (Cell i2 v2 _) = i1 == i2 && v1 == v2
 
 instance Show Cell where
   show (Cell ix val _) = "<" ++ show ix ++ " " ++ show val ++ ">"
 
 instance Ord Cell where
-  (Cell i1 v1 vl1) `compare` (Cell i2 v2 vl2)
-    | i1 == i2 && v1 == v2 = EQ
-    | otherwise            = (vl1, i1) `compare`(vl2, i2)
+  (Cell i1 v1 vl1) `compare` (Cell i2 v2 vl2) =
+    if i1 == i2 && v1 == v2
+    then EQ
+    else (vl1, i1) `compare`(vl2, i2)
 
 emptyBoard :: Board
 emptyBoard =
@@ -39,10 +43,11 @@ emptyBoard =
 updateBoard :: Board -> Cell -> Board
 updateBoard board@Board{..} cell@(Cell ix _ vl) = case M.lookup ix ixMap of
   Nothing      -> board
-  Just oldCell | vl == 1   -> Board (M.insert ix cell ixMap)
-                                    (S.delete oldCell ambCells)
-               | otherwise -> Board (M.insert ix cell ixMap)
-                                    (S.insert cell (S.delete oldCell ambCells))
+  Just oldCell | oldCell == cell -> board
+               | vl == 1         -> Board (M.insert ix cell ixMap)
+                                          (S.delete oldCell ambCells)
+               | otherwise       -> Board (M.insert ix cell ixMap)
+                                          (S.insert cell (S.delete oldCell ambCells))
 
 constrainCell :: Cell -> Board -> Cell -> Maybe Board
 constrainCell cell@(Cell _ val vl) board@Board{..} c@(Cell i pos pl) =
@@ -53,9 +58,18 @@ constrainCell cell@(Cell _ val vl) board@Board{..} c@(Cell i pos pl) =
               | pl' == 1 && pl > 1   -> constrainBoard board (Cell i pos' pl')
               | otherwise            -> return $ updateBoard board (Cell i pos' pl')
   where
-    pos' = pos \\ val
+    pos' = diff pos val
     pl' = length pos'
 
+    diff :: [Int] -> [Int] -> [Int]
+    diff [] [] = []
+    diff xs [] = xs
+    diff [] _  = []
+    diff xa@(x:xs) ya@(y:ys)
+      | x == y = diff xs ys
+      | x < y  = x : diff xs ya
+      | x > y  = diff xa ys
+
 constrainCells :: Cell -> Board -> [Cell] -> Maybe Board
 constrainCells cell = foldM (constrainCell cell)
 
@@ -83,7 +97,7 @@ readBoard str =
 showBoard :: Board -> String
 showBoard board =
   zipWith (\(Cell _ val vl) dot -> if vl == 1 then intToDigit (head val) else dot)
-          (map snd . M.toList . ixMap $ board)
+          (M.elems . ixMap $ board)
           (repeat '.')
 
 printBoard :: Board -> IO ()
@@ -113,21 +127,28 @@ solveSudoku board
                            Just board''  -> Just board''
                            Nothing       -> solveSudoku boardR
   where
-    ((Cell ix val vl), cs) = S.deleteFindMin (ambCells board)
+    (Cell ix val vl, cs) = S.deleteFindMin (ambCells board)
     isSolved = all (\(Cell _ _ vl) -> vl == 1) . M.elems . ixMap
 
 main :: IO ()
 main = do
-  lns <- fmap lines getContents
-  forM_ lns $ \line -> forkIO $ do
-    start <- getCPUTime
-    let sudoku = readBoard line
-    case sudoku of
-      Nothing -> putStrLn ("Invalid input sudoku: " ++ line)
-      Just board -> do
-        let !res = solveSudoku board
-        end <- getCPUTime
-        let diff = fromIntegral (end - start) / (10 ^ 12)
+  chunks <- fmap (chunksOf 50 . lines) getContents
+  threads <- forM chunks $ \chunk -> do
+              done <- newEmptyMVar
+              forkIO $ do
+                forM_ chunk $ \line -> do
+                  start <- getCPUTime
+                  let sudoku = readBoard line
+                  case sudoku of
+                    Nothing -> putStrLn ("Invalid input sudoku: " ++ line)
+                    Just board -> do
+                      let !res = solveSudoku board
+                      end <- getCPUTime
+                      let diff = fromIntegral (end - start) / (10 ^ 9)
 
-        putStrLn (printf "%s -> %s [%0.3f sec]" line
-                 (maybe "Unsolvable" showBoard res) (diff :: Double))
\ No newline at end of file
+                      putStrLn (printf "%s -> %s [%0.3f ms]" line
+                               (maybe "Unsolvable" showBoard res) (diff :: Double))
+                putMVar done ()
+              return done
+
+  mapM_ takeMVar threads
diff --git a/rubyquiz.cabal b/rubyquiz.cabal
index 01bd659..6f3e137 100644
--- a/rubyquiz.cabal
+++ b/rubyquiz.cabal
@@ -85,7 +85,7 @@ executable SudokuSolver
                       containers == 0.4.*,
                       mtl == 2.1.*,
                       split == 0.2.1.*,
-                      array == 0.4.*
+                      unordered-containers == 0.2.1.*
   main-is           : SudokuSolver.hs
   ghc-options       : -threaded
   default-language  : Haskell2010
\ No newline at end of file