From f9bb4cf8692e408c97f27e00d9287c18e96bd9af Mon Sep 17 00:00:00 2001
From: Correl Roush <correl@gmail.com>
Date: Fri, 31 Aug 2012 00:58:30 -0400
Subject: [PATCH] Level 1 - Tic Tac Toe

---
 TicTacToe.hs | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 TicTacToe.hs

diff --git a/TicTacToe.hs b/TicTacToe.hs
new file mode 100644
index 0000000..48ed1a6
--- /dev/null
+++ b/TicTacToe.hs
@@ -0,0 +1,74 @@
+module Main where
+
+import Data.List (sort, findIndices)
+import System.Random (randomRIO)
+
+testboard :: String
+testboard = "O_X_X_O__"
+
+getList :: Int -> IO [String]
+getList n = if n==0 then return [] else do i <- getLine; is <- getList(n-1); return (i:is)
+
+findEmpty :: String -> [Int]
+findEmpty board = findIndices (\c -> c == '_') board
+
+sets :: [[Int]]
+sets = [[0,1,2],
+        [3,4,5],
+        [6,7,8],
+        
+        [0,3,6],
+        [1,4,7],
+        [2,5,8],
+        
+        [0,4,8],
+        [2,4,6]]
+
+findMoves :: String -> Char -> [(Int, Int)]
+findMoves board player = moves
+  where moves = [(scoreIndex i, i) | i <- indexes]
+        indexes = findEmpty board
+        scoreIndex x = sum $ map (scoreSet player) $ findSets board x
+
+bestMoves :: [(Int, Int)] -> [Int]
+bestMoves [] = []
+bestMoves moves = [snd m | m <- sortedMoves, bestScore == fst m]
+  where sortedMoves = reverse.sort $ moves
+        bestScore = fst $ head sortedMoves
+
+findSets :: String -> Int -> [String]
+findSets board index = sets''
+  where sets' = filter (\x -> elem index x) sets 
+        sets'' = map chars' sets'
+        chars' = map (\x -> board !! x)
+
+scoreSet :: Char -> String -> Int
+scoreSet player set
+  | (elem 'O' set) && (elem 'X' set) = 0
+  | otherwise = 2 ^ (length.filter (\x -> x /= '_') $ set)
+
+otherPlayer :: Char -> Char
+otherPlayer 'X' = 'O'
+otherPlayer 'O' = 'X'
+
+coords :: Int -> (Int, Int)
+coords index = (y, x)
+  where y = index `div` 3
+        x = index `rem` 3
+
+main = do
+
+    -- If player is X, I'm the first player.
+    -- If player is O, I'm the second player.
+    player <- getLine
+
+    -- Read the board now. The board is a list of strings filled with X, O or _.
+    board <- getList 3
+
+    let moves = bestMoves $ findMoves (concat board) (player !! 0)
+    r <- randomRIO (1, length(moves))
+    let nextMove = coords $ moves !! (r - 1)
+    
+    -- Proceed with processing and print 2 integers separated by a single space.
+    putStrLn.(\(x, y) -> show x ++ " " ++ show y) $ nextMove
+