added enum

PuzzlePlayer/Board.cs

@@ -8,6 +8,13 @@ using System.Windows.Forms;
 
 namespace PuzzlePlayer_Namespace
 {
+    public enum SOLUTIONS
+    {
+        NONE = 0,
+        UNIQUE = 1,
+        MULTIPLE = 2
+    }
+
     /*
      * This abstract class can be used to implement any kind of puzzle
      * One thing that is common for all puzzles is that a empty space is equal to -1
@@ -22,14 +29,28 @@ namespace PuzzlePlayer_Namespace
         public int[,] boardState
         {
             get { return boardState; }
-            set { if (IsBoardValid(value) && Solve(value) != null) boardState = value; } // checks if the board is valid and solvable before setting the variable.
+            set { setBoardState(value); } 
+        }
+
+        // checks if the board is valid and solvable before setting the variable.
+        private bool setBoardState(int[,] newState)
+        {
+            int[,] copy = boardState;
+            boardState = newState;
+            if (IsBoardValid(newState) && Solve() == SOLUTIONS.UNIQUE)
+                return true;
+            else
+            {
+                boardState = copy;
+                return false;
+            }
         }
 
         // a methode for solving the whole board. It uses the private SolveStep methode untill the whole board is solved
-        public Board Solve()
+        public SOLUTIONS Solve()
         {
             // two variables for storing the result and the next solveStep
-            int[,] result = boardToSolve;
+            int[,] result = boardState;
             int[,] step;
 
             // keep looping until the SolveStep returns null
@@ -44,9 +65,12 @@ namespace PuzzlePlayer_Namespace
             for (int i = 0; i < result.GetLength(0); i++)
                 for (int j = 0; j < result.GetLength(1); j++)
                     if (result[i, j] == emptySpace)
-                        return null;
+                    {
+                        return SOLUTIONS.NONE;
+                    }
 
-            return result;
+            boardState = result;
+            return SOLUTIONS.UNIQUE;
         }
 
         // abstract methode for solving one step