diff --git a/app/src/main/java/sudoku/solver/Solver.java b/app/src/main/java/sudoku/solver/Solver.java
index e1eb4b5..0a79cd1 100644
--- a/app/src/main/java/sudoku/solver/Solver.java
+++ b/app/src/main/java/sudoku/solver/Solver.java
@@ -11,11 +11,11 @@ public class Solver {
 
     /**
      * Résout le multidoku passé en paramètre si c'est possible.
-     * En testant toutes les possibilités avec un algorithme de backtracking.
+     * En testant toutes les possibilités, de manière aléatoire, avec un algorithme de backtracking.
      *
      * @param doku Multidoku, à résoudre
-     * @param rand random pour tester aléatoirement les symboles
-     * @return boolean, true s'il est résolut ou false s'il ne l'est pas.
+     * @param rand Random, pour tester aléatoirement les symboles
+     * @return boolean, true s'il est résolu ou false s'il ne l'est pas.
      */
     public static boolean solveRandom(MultiDoku doku, Random rand) {
         if (Thread.interrupted())
@@ -39,15 +39,40 @@ public class Solver {
             cellToFill.setSymbolIndex(nextSymbol);
             if (Solver.solveRandom(doku, rand)) {
                 return true;
-            } else {
-                cellToFill.setSymbolIndex(Cell.NOSYMBOL);
-                possibleSymbols.remove(nextPossibleSymbolIndex);
             }
+            cellToFill.setSymbolIndex(Cell.NOSYMBOL);
+            possibleSymbols.remove(nextPossibleSymbolIndex);
 
         }
         return false;
     }
 
+    public static int countSolution(MultiDoku doku) {
+        int result = 0;
+
+        if (doku.isValid()) {
+            return 1;
+        }
+
+        Cell cellToFill = doku.getFirstEmptyCell();
+        if (cellToFill == null) {
+            return 0;
+        }
+
+        List<Integer> possibleSymbols = doku.getPossibleSymbolsOfCell(cellToFill);
+
+        for (int symbol : possibleSymbols) {
+
+            cellToFill.setSymbolIndex(symbol);
+            if (Solver.solve(doku)) {
+                result++;
+            }
+            cellToFill.setSymbolIndex(Cell.NOSYMBOL);
+        }
+
+        return result;
+    }
+
     public static boolean solve(MultiDoku doku) {
         if (Thread.interrupted())
 			throw new CancellationException("User wants to stop the solver");
diff --git a/app/src/main/java/sudoku/structure/Cell.java b/app/src/main/java/sudoku/structure/Cell.java
index 758267c..58e7aeb 100644
--- a/app/src/main/java/sudoku/structure/Cell.java
+++ b/app/src/main/java/sudoku/structure/Cell.java
@@ -77,4 +77,10 @@ public class Cell {
 	public boolean isMutable() {
 		return this.isMutable;
 	}
+
+    public int empty() {
+		int oldSymbol = this.symbolIndex;
+		this.symbolIndex = Cell.NOSYMBOL;
+		return oldSymbol;
+    }
 }
diff --git a/app/src/main/java/sudoku/structure/MultiDoku.java b/app/src/main/java/sudoku/structure/MultiDoku.java
index cf68c69..5abfb11 100644
--- a/app/src/main/java/sudoku/structure/MultiDoku.java
+++ b/app/src/main/java/sudoku/structure/MultiDoku.java
@@ -98,5 +98,21 @@ public class MultiDoku {
 
 		return true;
 	}
+
+	public List<Cell> getFilledCells() {
+		List<Cell> result = new ArrayList<>();
+		for (Cell c : this.getCells()){
+			if (!c.isEmpty()) {
+				result.add(c);
+			}
+		}
+		return result;
+	}
+
+	public void empty(Cell cell) {
+		List<Cell> cells = getCells();
+		Cell cellToEmpty = cells.get(cells.indexOf(cell));
+		cellToEmpty.setSymbolIndex(Cell.NOSYMBOL);
+	}
 }
 
diff --git a/app/src/main/java/sudoku/structure/Sudoku.java b/app/src/main/java/sudoku/structure/Sudoku.java
index 1d24441..a56acb8 100644
--- a/app/src/main/java/sudoku/structure/Sudoku.java
+++ b/app/src/main/java/sudoku/structure/Sudoku.java
@@ -287,4 +287,8 @@ public class Sudoku {
 
 		return true;
 	}
+
+	public void empty(Cell cell) {
+
+	}
 }
diff --git a/app/src/main/java/sudoku/structure/SudokuFactory.java b/app/src/main/java/sudoku/structure/SudokuFactory.java
index f235c7a..86b3770 100644
--- a/app/src/main/java/sudoku/structure/SudokuFactory.java
+++ b/app/src/main/java/sudoku/structure/SudokuFactory.java
@@ -4,14 +4,17 @@ import sudoku.constraint.BlockConstraint;
 import sudoku.constraint.ColumnConstraint;
 import sudoku.constraint.IConstraint;
 import sudoku.constraint.LineConstraint;
-import sudoku.structure.*;
+import sudoku.solver.Solver;
 
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
+import java.util.Random;
 
 public class SudokuFactory {
 
+	private static final Random random = new Random();
+
 	private static List<Cell> initCells(int size) {
 		List<Cell> cells = new ArrayList<>(size * size);
 		for (int i = 0; i < size * size; i++) {
@@ -72,4 +75,35 @@ public class SudokuFactory {
 			}
 		});
 	}
+
+	public static boolean newDokuFromFilledOne (MultiDoku doku, int difficulty) throws Exception {
+
+		if (difficulty > doku.getCells().size()) {
+			throw new Exception();
+		}
+
+		if (difficulty == 0) {
+			return true;
+		}
+
+		List<Cell> cellsThatCanBeEmptied = doku.getFilledCells();
+
+		while (!cellsThatCanBeEmptied.isEmpty()) {
+			int index = random.nextInt(cellsThatCanBeEmptied.size());
+			Cell cellToEmpty = cellsThatCanBeEmptied.get(index);
+
+			int oldSymbol = cellToEmpty.empty();
+
+			if (Solver.countSolution(doku) == 1) {
+				if (newDokuFromFilledOne(doku, --difficulty)) {
+					return true;
+				}
+			}
+
+			cellToEmpty.setSymbolIndex(oldSymbol);
+			cellsThatCanBeEmptied.remove(cellToEmpty);
+		}
+
+		return false;
+    }
 }