aimacode · norvig · Mar 15, 2018 · Mar 6, 2018 · Mar 6, 2018 · Mar 6, 2018
diff --git a/search.py b/search.py
@@ -406,102 +406,75 @@ def astar_search(problem, h=None):
 
 class EightPuzzle(Problem):
 
-    """The problem of sliding tiles numbered from 1 to 8 on a 3x3 board,
+    """ The problem of sliding tiles numbered from 1 to 8 on a 3x3 board,
     where one of the squares is a blank. A state is represented as a 3x3 list,
-    where element at index i,j represents the tile number (0 if it's an empty square)."""
+    where element at index i,j represents the tile number (0 if it's an empty square) """
 
-    def __init__(self, initial, goal=None):
-        if goal:
-            self.goal = goal
-        else:
-            self.goal = [ [0,1,2], 
-                          [3,4,5], 
-                          [6,7,8] ]
+    def __init__(self, initial, goal=(1, 2, 3, 4, 5, 6, 7, 8, 0)):
+        """ Define goal state and initialize a problem """
+
+        self.goal = goal
         Problem.__init__(self, initial, goal)
 
     def find_blank_square(self, state):
         """Return the index of the blank square in a given state"""
-        for row in len(state):
-            for column in len(row):
-                if state[row][column] == 0:
-                    index_blank_square = (row, column)
-        return index_blank_square
+
+        return state.index(0)
 
     def actions(self, state):
-        """Return the actions that can be executed in the given state.
+        """ Return the actions that can be executed in the given state.
         The result would be a list, since there are only four possible actions
-        in any given state of the environment."""
-
-        possible_actions = list()
+        in any given state of the environment """
+        
+        possible_actions = ['UP', 'DOWN', 'LEFT', 'RIGHT']       
         index_blank_square = self.find_blank_square(state)
 
-        if index_blank_square(0) == 0:
-            possible_actions += ['DOWN']
-        elif index_blank_square(0) == 1:
-            possible_actions += ['UP', 'DOWN']
-        elif index_blank_square(0) == 2:
-            possible_actions += ['UP']
-
-        if index_blank_square(1) == 0:
-            possible_actions += ['RIGHT']
-        elif index_blank_square(1) == 1:
-            possible_actions += ['LEFT', 'RIGHT']
-        elif index_blank_square(1) == 2:
-            possible_actions += ['LEFT']
+        if index_blank_square % 3 == 0:
+            possible_actions.remove('LEFT')
+        if index_blank_square < 3:
+            possible_actions.remove('UP')
+        if index_blank_square % 3 == 2:
+            possible_actions.remove('RIGHT')
+        if index_blank_square > 5:
+            possible_actions.remove('DOWN')
 
         return possible_actions
 
     def result(self, state, action):
-        """Given state and action, return a new state that is the result of the action.
-        Action is assumed to be a valid action in the state."""
-
-        blank_square = self.find_blank_square(state)
-        new_state = [row[:] for row in state]
-
-        if action=='UP':
-            new_state[blank_square(0)][blank_square(1)] = new_state[blank_square(0)-1][blank_square(1)]
-            new_state[blank_square(0)-1][blank_square(1)] = 0
-        elif action=='LEFT':
-            new_state[blank_square(0)][blank_square(1)] = new_state[blank_square(0)][blank_square(1)-1]
-            new_state[blank_square(0)][blank_square(1)-1] = 0
-        elif action=='DOWN':
-            new_state[blank_square(0)][blank_square(1)] = new_state[blank_square(0)+1][blank_square(1)]
-            new_state[blank_square(0)+1][blank_square(1)] = 0
-        elif action=='RIGHT':
-            new_state[blank_square(0)][blank_square(1)] = new_state[blank_square(0)][blank_square(1)+1]
-            new_state[blank_square(0)][blank_square(1)+1] = 0
-        else:
-            print("Invalid Action!")
-        return new_state
+        """ Given state and action, return a new state that is the result of the action.
+        Action is assumed to be a valid action in the state """
+
+        # blank is the index of the blank square
+        blank = self.find_blank_square(state)
+        new_state = list(state)
+
+        delta = {'UP':-3, 'DOWN':3, 'LEFT':-1, 'RIGHT':1}
+        neighbor = blank + delta[action]
+        new_state[blank], new_state[neighbor] = new_state[neighbor], new_state[blank]
+
+        return tuple(new_state)
 
     def goal_test(self, state):
-        """Given a state, return True if state is a goal state or False, otherwise"""
-        for row in len(state):
-            for column in len(row):
-                if state[row][col] != self.goal[row][column]:
-                    return False
-        return True
-
-    def checkSolvability(self, state):
+        """ Given a state, return True if state is a goal state or False, otherwise """
+
+        return state == self.goal
+
+    def check_solvability(self, state):
+        """ Checks if the given state is solvable """
+
         inversion = 0
         for i in range(len(state)):
-               for j in range(i, len(state)):
-                    if (state[i] > state[j] and state[j] != 0):
-                                    inversion += 1
-        check = True
-        if inversion%2 != 0:
-                check = False
-        print(check)
+            for j in range(i, len(state)):
+                if (state[i] > state[j] and state[j] != 0):
+                    inversion += 1
+
+        return (inversion % 2 == 0)
 
-    def h(self, state):
-        """Return the heuristic value for a given state. Heuristic function used is 
-        h(n) = number of misplaced tiles."""
-        num_misplaced_tiles = 0
-        for row in len(state):
-            for column in len(row):
-                if state[row][col] != self.goal[row][column]:
-                    num_misplaced_tiles += 1
-        return num_misplaced_tiles
+    def h(self, node):
+        """ Return the heuristic value for a given state. Default heuristic function used is 
+        h(n) = number of misplaced tiles """
+
+        return sum(s != g for (s, g) in zip(node.state, self.goal))
 
 # ______________________________________________________________________________
 # Other search algorithms

diff --git a/tests/test_search.py b/tests/test_search.py
@@ -5,6 +5,8 @@
 romania_problem = GraphProblem('Arad', 'Bucharest', romania_map)
 vacumm_world = GraphProblemStochastic('State_1', ['State_7', 'State_8'], vacumm_world)
 LRTA_problem = OnlineSearchProblem('State_3', 'State_5', one_dim_state_space)
+eight_puzzle = EightPuzzle((1, 2, 3, 4, 5, 7, 8, 6, 0))
+eight_puzzle2 = EightPuzzle((1, 0, 6, 8, 7, 5, 4, 2), (0, 1, 2, 3, 4, 5, 6, 7, 8))
 
 def test_find_min_edge():
     assert romania_problem.find_min_edge() == 70
@@ -64,6 +66,63 @@ def test_bidirectional_search():
 
 def test_astar_search():
     assert astar_search(romania_problem).solution() == ['Sibiu', 'Rimnicu', 'Pitesti', 'Bucharest']
+    assert astar_search(eight_puzzle).solution() == ['LEFT', 'LEFT', 'UP', 'RIGHT', 'RIGHT', 'DOWN', 'LEFT', 'UP', 'LEFT', 'DOWN', 'RIGHT', 'RIGHT']
+    assert astar_search(EightPuzzle((1, 2, 3, 4, 5, 6, 0, 7, 8))).solution() == ['RIGHT', 'RIGHT']
+
+
+def test_find_blank_square():
+    assert eight_puzzle.find_blank_square((0, 1, 2, 3, 4, 5, 6, 7, 8)) == 0
+    assert eight_puzzle.find_blank_square((6, 3, 5, 1, 8, 4, 2, 0, 7)) == 7
+    assert eight_puzzle.find_blank_square((3, 4, 1, 7, 6, 0, 2, 8, 5)) == 5
+    assert eight_puzzle.find_blank_square((1, 8, 4, 7, 2, 6, 3, 0, 5)) == 7
+    assert eight_puzzle.find_blank_square((4, 8, 1, 6, 0, 2, 3, 5, 7)) == 4
+    assert eight_puzzle.find_blank_square((1, 0, 6, 8, 7, 5, 4, 2, 3)) == 1
+    assert eight_puzzle.find_blank_square((1, 2, 3, 4, 5, 6, 7, 8, 0)) == 8
+
+
+def test_actions():
+    assert eight_puzzle.actions((0, 1, 2, 3, 4, 5, 6, 7, 8)) == ['DOWN', 'RIGHT']
+    assert eight_puzzle.actions((6, 3, 5, 1, 8, 4, 2, 0, 7)) == ['UP', 'LEFT', 'RIGHT']
+    assert eight_puzzle.actions((3, 4, 1, 7, 6, 0, 2, 8, 5)) == ['UP', 'DOWN', 'LEFT']
+    assert eight_puzzle.actions((1, 8, 4, 7, 2, 6, 3, 0, 5)) == ['UP', 'LEFT', 'RIGHT']
+    assert eight_puzzle.actions((4, 8, 1, 6, 0, 2, 3, 5, 7)) == ['UP', 'DOWN', 'LEFT', 'RIGHT']
+    assert eight_puzzle.actions((1, 0, 6, 8, 7, 5, 4, 2, 3)) == ['DOWN', 'LEFT', 'RIGHT']
+    assert eight_puzzle.actions((1, 2, 3, 4, 5, 6, 7, 8, 0)) == ['UP', 'LEFT']
+
+
+def test_result():
+    assert eight_puzzle.result((0, 1, 2, 3, 4, 5, 6, 7, 8), 'DOWN') == (3, 1, 2, 0, 4, 5, 6, 7, 8)
+    assert eight_puzzle.result((6, 3, 5, 1, 8, 4, 2, 0, 7), 'LEFT') == (6, 3, 5, 1, 8, 4, 0, 2, 7)
+    assert eight_puzzle.result((3, 4, 1, 7, 6, 0, 2, 8, 5), 'UP') == (3, 4, 0, 7, 6, 1, 2, 8, 5)
+    assert eight_puzzle.result((1, 8, 4, 7, 2, 6, 3, 0, 5), 'RIGHT') == (1, 8, 4, 7, 2, 6, 3, 5, 0)
+    assert eight_puzzle.result((4, 8, 1, 6, 0, 2, 3, 5, 7), 'LEFT') == (4, 8, 1, 0, 6, 2, 3, 5, 7)
+    assert eight_puzzle.result((1, 0, 6, 8, 7, 5, 4, 2, 3), 'DOWN') == (1, 7, 6, 8, 0, 5, 4, 2, 3)
+    assert eight_puzzle.result((1, 2, 3, 4, 5, 6, 7, 8, 0), 'UP') == (1, 2, 3, 4, 5, 0, 7, 8, 6)
+    assert eight_puzzle.result((4, 8, 1, 6, 0, 2, 3, 5, 7), 'RIGHT') == (4, 8, 1, 6, 2, 0, 3, 5, 7)
+
+
+def test_goal_test():
+    assert eight_puzzle.goal_test((0, 1, 2, 3, 4, 5, 6, 7, 8)) == False
+    assert eight_puzzle.goal_test((6, 3, 5, 1, 8, 4, 2, 0, 7)) == False
+    assert eight_puzzle.goal_test((3, 4, 1, 7, 6, 0, 2, 8, 5)) == False
+    assert eight_puzzle.goal_test((1, 2, 3, 4, 5, 6, 7, 8, 0)) == True
+    assert eight_puzzle2.goal_test((4, 8, 1, 6, 0, 2, 3, 5, 7)) == False
+    assert eight_puzzle2.goal_test((3, 4, 1, 7, 6, 0, 2, 8, 5)) == False
+    assert eight_puzzle2.goal_test((1, 2, 3, 4, 5, 6, 7, 8, 0)) == False
+    assert eight_puzzle2.goal_test((0, 1, 2, 3, 4, 5, 6, 7, 8)) == True
+
+
+def test_check_solvability():
+    assert eight_puzzle.check_solvability((0, 1, 2, 3, 4, 5, 6, 7, 8)) == True
+    assert eight_puzzle.check_solvability((6, 3, 5, 1, 8, 4, 2, 0, 7)) == True
+    assert eight_puzzle.check_solvability((3, 4, 1, 7, 6, 0, 2, 8, 5)) == True
+    assert eight_puzzle.check_solvability((1, 8, 4, 7, 2, 6, 3, 0, 5)) == True
+    assert eight_puzzle.check_solvability((4, 8, 1, 6, 0, 2, 3, 5, 7)) == True
+    assert eight_puzzle.check_solvability((1, 0, 6, 8, 7, 5, 4, 2, 3)) == True
+    assert eight_puzzle.check_solvability((1, 2, 3, 4, 5, 6, 7, 8, 0)) == True
+    assert eight_puzzle.check_solvability((1, 2, 3, 4, 5, 6, 8, 7, 0)) == False
+    assert eight_puzzle.check_solvability((1, 0, 3, 2, 4, 5, 6, 7, 8)) == False
+    assert eight_puzzle.check_solvability((7, 0, 2, 8, 5, 3, 6, 4, 1)) == False
 
 
 def test_recursive_best_first_search():