diff --git a/Main.java b/Main.java
index b695b09..8fc9910 100644
--- a/Main.java
+++ b/Main.java
@@ -1,4 +1,6 @@
-import java.io.*;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
@@ -110,11 +112,32 @@ public class Main {
         for (int i = 0; i < numberOfChromosomes; i++) {
             // Create a copy of the base Sudoku
             int[][] sudoku = copyMatrix(baseSudoku);
-            // Randomly fill mutable positions
-            for (int[] pos : mutablePositions) {
-                int row = pos[0];
-                int col = pos[1];
-                sudoku[row][col] = random.nextInt(9) + 1;
+            // Randomly fill mutable positions while ensuring no duplicates in subgrids
+            for (int gridRow = 0; gridRow < 3; gridRow++) {
+                for (int gridCol = 0; gridCol < 3; gridCol++) {
+                    boolean[] present = new boolean[10];
+                    List<int[]> subgridPositions = new ArrayList<>();
+                    // Collect all positions in the current 3x3 subgrid
+                    for (int row = gridRow * 3; row < gridRow * 3 + 3; row++) {
+                        for (int col = gridCol * 3; col < gridCol * 3 + 3; col++) {
+                            int value = sudoku[row][col];
+                            if (value != 0) {
+                                present[value] = true;
+                            } else {
+                                subgridPositions.add(new int[]{row, col});
+                            }
+                        }
+                    }
+                    // Randomly fill the subgrid ensuring no duplicates
+                    for (int[] pos : subgridPositions) {
+                        int newValue;
+                        do {
+                            newValue = random.nextInt(9) + 1;
+                        } while (present[newValue]);
+                        sudoku[pos[0]][pos[1]] = newValue;
+                        present[newValue] = true;
+                    }
+                }
             }
             // Create a new chromosome with the generated Sudoku and mutable positions
             Chromosome chromosome = new Chromosome(sudoku, new ArrayList<>(mutablePositions));
@@ -123,6 +146,7 @@ public class Main {
         }
     }
 
+
     // Create a deep copy of a matrix
     private int[][] copyMatrix(int[][] original) {
         int[][] copy = new int[original.length][original[0].length];
@@ -205,15 +229,29 @@ public class Main {
     
     public void mutateChromosome(Chromosome chromosome, double mutationRate) {
         int[][] sudoku = chromosome.getSudoku();
-        List<int[]> mutablePositions = chromosome.getMutablePositions();
     
-        // Mutate each mutable position with a probability defined by mutationRate
-        for (int[] pos : mutablePositions) {
-            if (random.nextDouble() < mutationRate) {
-                int row = pos[0];
-                int col = pos[1];
-                int newValue = random.nextInt(9) + 1; // Assign a new value between 1 and 9
-                sudoku[row][col] = newValue;
+        // With a probability defined by mutationRate, perform a mutation by swapping subgrids
+        if (random.nextDouble() < mutationRate) {
+            // Randomly select two different subgrids to swap
+            int subgrid1, subgrid2;
+            do {
+                subgrid1 = random.nextInt(9);
+                subgrid2 = random.nextInt(9);
+            } while (subgrid1 == subgrid2);
+    
+            // Get the starting coordinates for both subgrids
+            int rowStart1 = (subgrid1 / 3) * 3;
+            int colStart1 = (subgrid1 % 3) * 3;
+            int rowStart2 = (subgrid2 / 3) * 3;
+            int colStart2 = (subgrid2 % 3) * 3;
+    
+            // Swap the values in the two selected subgrids
+            for (int rowOffset = 0; rowOffset < 3; rowOffset++) {
+                for (int colOffset = 0; colOffset < 3; colOffset++) {
+                    int temp = sudoku[rowStart1 + rowOffset][colStart1 + colOffset];
+                    sudoku[rowStart1 + rowOffset][colStart1 + colOffset] = sudoku[rowStart2 + rowOffset][colStart2 + colOffset];
+                    sudoku[rowStart2 + rowOffset][colStart2 + colOffset] = temp;
+                }
             }
         }
     
@@ -222,6 +260,7 @@ public class Main {
         chromosome.evaluateFitness();
     }
     
+    
     public void evaluatePopulation() {
         // Evaluate the fitness of each chromosome in the population
         for (Chromosome chromosome : population) {
diff --git a/statistical/demo/src/main/java/com/example/Main.java b/statistical/demo/src/main/java/com/example/Main.java
index 4258789..40dc4d8 100644
--- a/statistical/demo/src/main/java/com/example/Main.java
+++ b/statistical/demo/src/main/java/com/example/Main.java
@@ -1,8 +1,11 @@
 package com.example;
-import java.io.*;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
+
 import org.knowm.xchart.SwingWrapper;
 import org.knowm.xchart.XYChart;
 import org.knowm.xchart.XYSeries;
@@ -126,7 +129,7 @@ public class Main {
             // Randomly fill mutable positions
             for (int[] pos : mutablePositions) {
                 int row = pos[0];
-                int col = pos[1];
+                int col = pos[1];   
                 sudoku[row][col] = random.nextInt(9) + 1;
             }
             // Create a new chromosome with the generated Sudoku and mutable positions
diff --git a/statistical/demo/target/classes/Main$Chromosome.class b/statistical/demo/target/classes/Main$Chromosome.class
deleted file mode 100644
index 77b54fe..0000000
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diff --git a/statistical/demo/target/classes/Main.class b/statistical/demo/target/classes/Main.class
deleted file mode 100644
index 257a34b..0000000
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diff --git a/statistical/demo/target/classes/com/example/Main$Chromosome.class b/statistical/demo/target/classes/com/example/Main$Chromosome.class
index cf9d0a4..ad09172 100644
Binary files a/statistical/demo/target/classes/com/example/Main$Chromosome.class and b/statistical/demo/target/classes/com/example/Main$Chromosome.class differ
diff --git a/statistical/demo/target/classes/com/example/Main.class b/statistical/demo/target/classes/com/example/Main.class
index 27b60fa..b63c52e 100644
Binary files a/statistical/demo/target/classes/com/example/Main.class and b/statistical/demo/target/classes/com/example/Main.class differ