diff --git a/GUI.py b/GUI.py
index d39a705..fec5e45 100644
--- a/GUI.py
+++ b/GUI.py
@@ -4,6 +4,7 @@
 pygame.font.init()
 
 
+
 class Grid:
     board = [
         [7, 8, 0, 4, 0, 0, 1, 2, 0],
@@ -16,34 +17,71 @@ class Grid:
         [1, 2, 0, 0, 0, 7, 4, 0, 0],
         [0, 4, 9, 2, 0, 6, 0, 0, 7]
     ]
+    
 
     def __init__(self, rows, cols, width, height, win):
         self.rows = rows
         self.cols = cols
         self.cubes = [[Cube(self.board[i][j], i, j, width, height) for j in range(cols)] for i in range(rows)]
+        self.row_sets = [set() for _ in range(9)]    
+        self.box_sets = [set() for _ in range(9)]
+        self.col_sets = [set() for _ in range(9)]
         self.width = width
         self.height = height
-        self.model = None
-        self.update_model()
         self.selected = None
         self.win = win
-
-    def update_model(self):
-        self.model = [[self.cubes[i][j].value for j in range(self.cols)] for i in range(self.rows)]
+        for i in range(9):
+            for j in range(9):
+                if self.board[i][j] != 0:
+                    val = self.board[i][j]
+                    box_index = (i // 3) * 3 + (j // 3)
+                    self.row_sets[i].add(val)
+                    self.col_sets[j].add(val)
+                    self.box_sets[box_index].add(val)
+
+    def valid(self, val,pos):
+        row, col = pos
+        box_index = (row//3) * 3 + (col//3)
+        if val in self.col_sets[col] or val in self.row_sets[row] or val in self.box_sets[box_index]:
+                return False
+        
+        return True
 
     def place(self, val):
         row, col = self.selected
         if self.cubes[row][col].value == 0:
-            self.cubes[row][col].set(val)
-            self.update_model()
+            box_index = (row//3) * 3 + (col//3)
 
-            if valid(self.model, val, (row,col)) and self.solve():
-                return True
-            else:
-                self.cubes[row][col].set(0)
-                self.cubes[row][col].set_temp(0)
-                self.update_model()
+            if val in self.col_sets[col] or val in self.row_sets[row] or val in self.box_sets[box_index]:
                 return False
+            
+            self.cubes[row][col].set(val)
+            self.col_sets[col].add(val)
+            self.row_sets[row].add(val)
+            self.box_sets[box_index].add(val)
+            
+            return True
+        
+        return False
+    
+    def remove_number(self):
+        row, col = self.selected
+        if self.cubes[row][col].value != 0:  
+            val = self.cubes[row][col].value  
+            box_index = (row//3) * 3 + (col//3)  
+
+            if val in self.row_sets[row]:
+                self.row_sets[row].remove(val)
+            if val in self.col_sets[col]:
+                self.col_sets[col].remove(val)
+            if val in self.box_sets[box_index]:
+                self.box_sets[box_index].remove(val)
+    
+            self.cubes[row][col].set(0)  
+            self.cubes[row][col].set_temp(0)  
+            return True  
+        return False
+
 
     def sketch(self, val):
         row, col = self.selected
@@ -93,54 +131,70 @@ def click(self, pos):
             return None
 
     def is_finished(self):
-        for i in range(self.rows):
-            for j in range(self.cols):
-                if self.cubes[i][j].value == 0:
-                    return False
+        for row_set in self.row_sets:
+            if len(row_set) != 9:
+                return False
         return True
 
     def solve(self):
-        find = find_empty(self.model)
+        temp_model = [[self.cubes[i][j].value for j in range(self.cols)] for i in range(self.rows)]
+        find = find_empty(temp_model)
         if not find:
             return True
         else:
             row, col = find
 
         for i in range(1, 10):
-            if valid(self.model, i, (row, col)):
-                self.model[row][col] = i
+            if self.valid(i, (row, col)):
+                box_index = (row//3) * 3 + (col//3)
+                self.row_sets[row].add(i)
+                self.col_sets[col].add(i)
+                self.box_sets[box_index].add(i)
+                temp_model[row][col] = i
 
                 if self.solve():
                     return True
-
-                self.model[row][col] = 0
+                
+                self.row_sets[row].remove(i)
+                self.col_sets[col].remove(i)
+                self.box_sets[box_index].remove(i)
+                temp_model[row][col] = 0
 
         return False
 
     def solve_gui(self):
-        self.update_model()
-        find = find_empty(self.model)
+        temp_model = [[self.cubes[i][j].value for j in range(self.cols)] for i in range(self.rows)]
+        find = find_empty(temp_model)
         if not find:
             return True
         else:
             row, col = find
 
         for i in range(1, 10):
-            if valid(self.model, i, (row, col)):
-                self.model[row][col] = i
+            if self.valid(i, (row, col)):
+                box_index = (row//3) * 3 + (col//3)
+            
+                self.row_sets[row].add(i)
+                self.col_sets[col].add(i)
+                self.box_sets[box_index].add(i)
+                
+                temp_model[row][col] = i
                 self.cubes[row][col].set(i)
                 self.cubes[row][col].draw_change(self.win, True)
-                self.update_model()
+
                 pygame.display.update()
                 pygame.time.delay(100)
 
                 if self.solve_gui():
                     return True
-
-                self.model[row][col] = 0
+                
+                self.row_sets[row].remove(i)
+                self.col_sets[col].remove(i)
+                self.box_sets[box_index].remove(i)
+                temp_model[row][col] = 0
                 self.cubes[row][col].set(0)
-                self.update_model()
                 self.cubes[row][col].draw_change(self.win, False)
+
                 pygame.display.update()
                 pygame.time.delay(100)
 
@@ -209,29 +263,6 @@ def find_empty(bo):
     return None
 
 
-def valid(bo, num, pos):
-    # Check row
-    for i in range(len(bo[0])):
-        if bo[pos[0]][i] == num and pos[1] != i:
-            return False
-
-    # Check column
-    for i in range(len(bo)):
-        if bo[i][pos[1]] == num and pos[0] != i:
-            return False
-
-    # Check box
-    box_x = pos[1] // 3
-    box_y = pos[0] // 3
-
-    for i in range(box_y*3, box_y*3 + 3):
-        for j in range(box_x * 3, box_x*3 + 3):
-            if bo[i][j] == num and (i,j) != pos:
-                return False
-
-    return True
-
-
 def redraw_window(win, board, time, strikes):
     win.fill((255,255,255))
     # Draw time
@@ -306,8 +337,11 @@ def main():
                     key = 8
                 if event.key == pygame.K_KP9:
                     key = 9
-                if event.key == pygame.K_DELETE:
-                    board.clear()
+                if event.key == pygame.K_d:
+                    if board.remove_number():
+                        print("number removed")
+                    else:
+                        board.clear()
                     key = None
 
                 if event.key == pygame.K_SPACE: