state-of-tic-tac-toe: fix generator

exercises/practice/state-of-tic-tac-toe/.meta/Example.fs

@@ -16,12 +16,14 @@ type Board = Cell [,]
 let won (player: Cell) (board: Board) =
     let winning = [| player; player; player |]
 
-    Array.init 3 (fun i -> board[i, i]) = winning ||
-    Array.init 3 (fun i -> board[i, 2 - i]) = winning
-    || Array.init 3 (fun i -> board[i, *]) |> Array.contains winning
-    || Array.init 3 (fun i -> board[*, i]) |> Array.contains winning
-
-let gameState (board: Board) =
+    Array.init 3 (fun i -> board[i, i]) = winning
+    || Array.init 3 (fun i -> board[i, 2 - i]) = winning
+    || Array.init 3 (fun i -> board[i, *])
+       |> Array.contains winning
+    || Array.init 3 (fun i -> board[*, i])
+       |> Array.contains winning
+
+let gamestate (board: Board) =
     let numCells cell =
         board
         |> Seq.cast

exercises/practice/state-of-tic-tac-toe/StateOfTicTacToe.fs

@@ -1,7 +1,47 @@
 module StateOfTicTacToe
 
-// TODO: define the 'EndGameState' type
-// TODO: define the 'GameError' type
+type EndGameState =
+    | Win
+    | Draw
+    | Ongoing
 
-let gameState board =
-    failwith "Please implement the 'gameState' function"
+type GameError =
+    | ConsecutiveMovesBySamePlayer
+    | WrongPlayerStarted
+    | MoveMadeAfterGameWasDone
+
+type Cell = char
+type Board = Cell [,]
+
+let won (player: Cell) (board: Board) =
+    let winning = [| player; player; player |]
+
+    Array.init 3 (fun i -> board[i, i]) = winning
+    || Array.init 3 (fun i -> board[i, 2 - i]) = winning
+    || Array.init 3 (fun i -> board[i, *])
+       |> Array.contains winning
+    || Array.init 3 (fun i -> board[*, i])
+       |> Array.contains winning
+
+let gamestate (board: Board) =
+    let numCells cell =
+        board
+        |> Seq.cast
+        |> Seq.filter ((=) cell)
+        |> Seq.length
+
+    let numNaughts = numCells 'O'
+    let numCrosses = numCells 'X'
+
+    if abs (numCrosses - numNaughts) > 1 then
+        Error ConsecutiveMovesBySamePlayer
+    elif numNaughts > numCrosses then
+        Error WrongPlayerStarted
+    elif won 'X' board && won 'O' board then
+        Error MoveMadeAfterGameWasDone
+    elif won 'X' board || won 'O' board then
+        Ok Win
+    elif numNaughts + numCrosses = 9 then
+        Ok Draw
+    else
+        Ok Ongoing