lib/screens/home.dart

@@ -17,6 +17,23 @@ class Home extends StatelessWidget {
 
     if (myProvider.stateRunning) {
       menuActions = [
+        FlatButton(
+          child: Container(
+            decoration: BoxDecoration(
+              borderRadius: BorderRadius.circular(4),
+              border: Border.all(
+                color: Colors.blue,
+                width: 4,
+              ),
+            ),
+            margin: EdgeInsets.all(8),
+            child: Image(
+              image: AssetImage('assets/icons/button_help.png'),
+              fit: BoxFit.fill
+            ),
+          ),
+          onPressed: () => GameUtils.showTip(myProvider),
+        ),
         FlatButton(
           child: Container(
             decoration: BoxDecoration(

lib/utils/game_utils.dart

 import '../provider/data.dart';
 import '../utils/board_utils.dart';
+import '../utils/game_utils.dart';
 
 class GameUtils {
 
@@ -8,10 +9,90 @@ class GameUtils {
   }
 
   static Future<void> startGame(Data myProvider) async {
-    print('Start new game: ' + myProvider.size);
     myProvider.updateSize = myProvider.size;
     myProvider.updateStateRunning = true;
     myProvider.updateCells = BoardUtils.createEmptyBoard(myProvider.blockSizeHorizontal * myProvider.blockSizeVertical);
     BoardUtils.pickGrid(myProvider);
   }
+
+  static void showTip(Data myProvider) {
+    if (myProvider.currentCellCol == null || myProvider.currentCellRow == null) {
+      // no selected cell -> pick one
+      GameUtils.helpSelectCell(myProvider);
+    } else {
+      // currently selected cell -> set value
+      GameUtils.helpFillCell(myProvider);
+    }
+  }
+
+  static void helpSelectCell(Data myProvider) {
+    List cells = myProvider.cells;
+    int boardSize = myProvider.blockSizeHorizontal * myProvider.blockSizeVertical;
+
+    // pick one of conflicting cells, if found
+    List conflictingCells = [];
+    for (var row = 0; row < boardSize; row++) {
+      for (var col = 0; col < boardSize; col++) {
+        if (!cells[row][col].isFixed && cells[row][col].value != 0) {
+
+          if (cells[row][col].conflictsCount != 0 && !BoardUtils.isValueAllowed(myProvider, col, row, cells[row][col].value)) {
+            conflictingCells.add([col, row]);
+          }
+        }
+      }
+    }
+    if (conflictingCells.length != 0) {
+      GameUtils.pickRandomFromList(myProvider, conflictingCells);
+      return;
+    }
+
+    //  pick one form cells with unique non-conflicting candidate value
+    List candidateCells = [];
+    for (var row = 0; row < boardSize; row++) {
+      for (var col = 0; col < boardSize; col++) {
+        if (cells[row][col].value == 0) {
+          int allowedValuesCount = 0;
+          for (var value = 1; value <= boardSize; value++) {
+            if (BoardUtils.isValueAllowed(myProvider, col, row, value)) {
+              allowedValuesCount++;
+            }
+          }
+          if (allowedValuesCount == 1) {
+            candidateCells.add([col, row]);
+          }
+        }
+      }
+    }
+    if (candidateCells.length != 0) {
+      GameUtils.pickRandomFromList(myProvider, candidateCells);
+      return;
+    }
+  }
+
+  static void pickRandomFromList(Data myProvider, List cellsCoordinates) {
+    if (cellsCoordinates.length > 0) {
+      cellsCoordinates.shuffle();
+      List cell = cellsCoordinates[0];
+      myProvider.selectCell(cell[0], cell[1]);
+    }
+  }
+
+  static void helpFillCell(Data myProvider) {
+    int boardSize = myProvider.blockSizeHorizontal * myProvider.blockSizeVertical;
+
+    int eligibleValue = 0;
+
+    // ensure there is only one eligible value for this cell
+    int allowedValuesCount = 0;
+    for (var value = 1; value <= boardSize; value++) {
+      if (BoardUtils.isValueAllowed(myProvider, myProvider.currentCellCol, myProvider.currentCellRow, value)) {
+        allowedValuesCount++;
+        eligibleValue = value;
+      }
+    }
+
+    myProvider.updateCellValue(myProvider.currentCellCol, myProvider.currentCellRow, allowedValuesCount == 1 ? eligibleValue : 0);
+    myProvider.selectCell(null, null);
+    BoardUtils.computeConflictsInBoard(myProvider);
+  }
 }