refactor MixedSolver

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

@@ -1,7 +1,6 @@
 package sudoku.solver;
 
 import java.util.List;
-import java.util.Random;
 import java.util.concurrent.CancellationException;
 
 import sudoku.structure.Cell;
@@ -9,6 +8,19 @@ import sudoku.structure.MultiDoku;
 
 public class MixedSolver implements Solver {
 
+    private Cell findCellToBacktrack(MultiDoku doku, int maxPossibilities) {
+        for (Cell cell : doku.getCells()) {
+            if (!cell.isMutable() || !cell.isEmpty())
+                continue;
+
+            List<Integer> possibleSymbols = cell.getPossibleSymbols();
+            if (possibleSymbols.size() == maxPossibilities) {
+                return cell;
+            }
+        }
+        return null;
+    }
+
     /**
      * Résout le MultiDoku passé en paramètre, avec règles de déduction et
      * backtracking.
@@ -18,47 +30,45 @@ public class MixedSolver implements Solver {
      */
     @Override
     public boolean solve(MultiDoku doku, List<SolverStep> steps) {
-        Random rand = new Random();
-
         if (Thread.interrupted()) {
             throw new CancellationException("User wants to stop the solver");
         }
 
-        if (doku.isSolved()) {
-            return true;
-        }
+        while (!doku.isSolved()) {
+            boolean filledCell = false;
+            for (Cell cell : doku.getCells()) {
+                if (!cell.isMutable() || !cell.isEmpty())
+                    continue;
 
-        Cell cellToFill = doku.getFirstEmptyCell();
-        if (cellToFill == null) {
-            return false;
-        }
-
-        List<Integer> possibleSymbols = cellToFill.getPossibleSymbols();
-
-        if (possibleSymbols.size() == 1) {
-            cellToFill.setSymbolIndex(possibleSymbols.getFirst());
-            addStep(cellToFill, steps);
-            if (this.solve(doku, steps)) {
-                return true;
+                List<Integer> possibleSymbols = cell.getPossibleSymbols();
+                if (possibleSymbols.size() == 1) {
+                    cell.setSymbolIndex(possibleSymbols.getFirst());
+                    addStep(cell, steps);
+                    filledCell = true;
+                }
             }
-        }
-
-        while (!possibleSymbols.isEmpty()) {
-            int nextPossibleSymbolIndex = rand.nextInt(possibleSymbols.size());
-            int nextSymbol = possibleSymbols.get(nextPossibleSymbolIndex);
-
-            cellToFill.setSymbolIndex(nextSymbol);
-            addStep(cellToFill, steps);
-            if (this.solve(doku, steps)) {
-                return true;
+            // 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();
+                }
             }
-            cellToFill.setSymbolIndex(Cell.NOSYMBOL);
-            addStep(cellToFill, steps);
-            possibleSymbols.remove(nextPossibleSymbolIndex);
 
         }
 
-        return false;
+        return true;
     }
 
 }