fix mixedsolver

app/src/main/java/sudoku/solver/MixedSolver.java

@@ -1,5 +1,6 @@
 package sudoku.solver;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.CancellationException;
 
@@ -8,17 +9,22 @@ import sudoku.structure.MultiDoku;
 
 public class MixedSolver implements Solver {
 
-    private Cell findCellToBacktrack(MultiDoku doku, int maxPossibilities) {
+    private List<Cell> findCellsToBacktrack(MultiDoku doku, int maxPossibilities) {
+        List<Cell> cells = new ArrayList<>();
         for (Cell cell : doku.getCells()) {
             if (!cell.isMutable() || !cell.isEmpty())
                 continue;
 
             List<Integer> possibleSymbols = cell.getPossibleSymbols();
             if (possibleSymbols.size() == maxPossibilities) {
-                return cell;
+                cells.add(cell);
             }
+
+            // une cellule nous empêche de continuer
+            if (possibleSymbols.size() == 0)
+                return null;
         }
-        return null;
+        return cells;
     }
 
     /**
@@ -34,41 +40,51 @@ public class MixedSolver implements Solver {
             throw new CancellationException("User wants to stop the solver");
         }
 
-        while (!doku.isSolved()) {
-            boolean filledCell = false;
-            for (Cell cell : doku.getCells()) {
-                if (!cell.isMutable() || !cell.isEmpty())
-                    continue;
+        if (doku.isSolved())
+            return true;
 
-                List<Integer> possibleSymbols = cell.getPossibleSymbols();
-                if (possibleSymbols.size() == 1) {
-                    cell.setSymbolIndex(possibleSymbols.getFirst());
-                    addStep(cell, steps);
-                    filledCell = true;
-                }
+        if (findCellsToBacktrack(doku, 0) == null)
+            return false;
+
+        for (Cell cell : doku.getCells()) {
+            if (!cell.isMutable() || !cell.isEmpty())
+                continue;
+
+            List<Integer> possibleSymbols = cell.getPossibleSymbols();
+            if (possibleSymbols.size() == 1) {
+                cell.setSymbolIndex(possibleSymbols.getFirst());
+                addStep(cell, steps);
+                if (solve(doku, steps))
+                    return true;
+                cell.setSymbolIndex(Cell.NOSYMBOL);
+                addStep(cell, steps);
+                return false;
             }
-            // on ne peut plus remplir de cases, on tente de backtrack
-            if (!filledCell) {
-                int maxPossibilities = 2;
-                Cell backtrackCell = null;
-                while (backtrackCell == null) {
-                    backtrackCell = findCellToBacktrack(doku, maxPossibilities);
-                    maxPossibilities++;
-                }
-                // on fait du backtracking
-                List<Integer> possibilities = backtrackCell.getPossibleSymbols();
-                for (int symbol : possibilities) {
-                    doku.getStateManager().pushState();
-                    backtrackCell.setSymbolIndex(symbol);
-                    if (solve(doku, steps))
-                        return true;
-                    doku.getStateManager().popState();
-                }
+        }
+        // on ne peut plus remplir de cases, on tente de backtrack
+        int maxPossibilities = 2;
+        List<Cell> backtrackCells = new ArrayList<>();
+        while (backtrackCells.isEmpty()) {
+            backtrackCells = findCellsToBacktrack(doku, maxPossibilities);
+            if (backtrackCells == null || maxPossibilities > doku.getSubGrid(0).getSize())
+                return false;
+            maxPossibilities++;
+        }
+        // on fait du backtracking
+        for (Cell backtrackCell : backtrackCells) {
+            List<Integer> possibilities = backtrackCell.getPossibleSymbols();
+            for (int symbol : possibilities) {
+                backtrackCell.setSymbolIndex(symbol);
+                addStep(backtrackCell, steps);
+                if (solve(doku, steps))
+                    return true;
             }
 
+            backtrackCell.setSymbolIndex(Cell.NOSYMBOL);
+            addStep(backtrackCell, steps);
         }
 
-        return true;
+        return false;
     }
 
 }