diff --git a/search.py b/search.py
index f177adc..dfb912d 100644
--- a/search.py
+++ b/search.py
@@ -4,7 +4,6 @@ Pacman agents (in searchAgents.py).
 
 Please only change the parts of the file you are asked to.  Look for the lines
 that say
-
 "*** YOUR CODE HERE ***"
 
 Follow the project description for details.
@@ -88,7 +87,7 @@ def depthFirstSearch(problem: SearchProblem):
     curr_state = problem.getStartState()
     isGoal = problem.isGoalState(curr_state)
 
-    visited = set([curr_state])
+    visited = list([curr_state])
     stack = util.Stack()
 
     while not isGoal:
@@ -107,7 +106,7 @@ def depthFirstSearch(problem: SearchProblem):
         else:
             obj = stack.pop()
             (curr_state, direction, cost) = obj['state']
-            visited.add(curr_state)
+            visited.append(curr_state)
             actions = obj['actions'] + [ direction ]
             isGoal = problem.isGoalState(curr_state)
 
@@ -123,15 +122,16 @@ def breadthFirstSearch(problem: SearchProblem):
     curr_state = problem.getStartState()
     isGoal = problem.isGoalState(curr_state)
 
-    visited = set([curr_state])
+    visited = list([curr_state])
     queue = util.Queue()
 
     while not isGoal:
+        print(curr_state)
         # push in the Stack
         successors = problem.getSuccessors(curr_state)
         for (state, direction, cost) in successors:
             if state not in visited:
-                visited.add(state)
+                visited.append(state)
                 queue.push({
                     'state': (state, direction, cost),
                     'actions': actions
@@ -158,7 +158,7 @@ def uniformCostSearch(problem: SearchProblem):
     isGoal = problem.isGoalState(curr_state)
     costs = 0
 
-    visited = set([curr_state])
+    visited = list([curr_state])
     queue = util.PriorityQueue()
 
     while not isGoal:
@@ -178,7 +178,7 @@ def uniformCostSearch(problem: SearchProblem):
         else:
             obj = queue.pop()
             (curr_state, direction, cost) = obj['state']
-            visited.add(curr_state)
+            visited.append(curr_state)
             actions = obj['actions'] + [ direction ]
             costs = obj['costs'] + cost
 
@@ -203,7 +203,7 @@ def aStarSearch(problem: SearchProblem, heuristic=nullHeuristic):
     isGoal = problem.isGoalState(curr_state)
     costs = 0
 
-    visited = set([curr_state])
+    visited = list([curr_state])
     queue = util.PriorityQueue()
 
     while not isGoal:
@@ -223,7 +223,7 @@ def aStarSearch(problem: SearchProblem, heuristic=nullHeuristic):
         else:
             obj = queue.pop()
             (curr_state, direction, cost) = obj['state']
-            visited.add(curr_state)
+            visited.append(curr_state)
             actions = obj['actions'] + [ direction ]
             costs = obj['costs'] + cost
 
diff --git a/searchAgents.py b/searchAgents.py
index 1d7ed89..cd03099 100644
--- a/searchAgents.py
+++ b/searchAgents.py
@@ -281,14 +281,17 @@ class CornersProblem(search.SearchProblem):
         space)
         """
         "*** YOUR CODE HERE ***"
-        util.raiseNotDefined()
+        return {
+                'position': self.startingPosition,
+                'target_corners': self.corners,
+            }
 
     def isGoalState(self, state: Any):
         """
         Returns whether this search state is a goal state of the problem.
         """
         "*** YOUR CODE HERE ***"
-        util.raiseNotDefined()
+        return len(state['target_corners']) == 0
 
     def getSuccessors(self, state: Any):
         """
@@ -311,7 +314,24 @@ class CornersProblem(search.SearchProblem):
             #   hitsWall = self.walls[nextx][nexty]
 
             "*** YOUR CODE HERE ***"
+            x, y = state['position']
+            dx, dy = Actions.directionToVector(action)
+            nextx, nexty = int(x + dx), int(y + dy)
+            hitsWall = self.walls[nextx][nexty]
 
+            if not hitsWall:
+                # new state (position, corners)
+                if (nextx, nexty) in state['target_corners']:
+                    new_corners = tuple( i for i in state['target_corners'] if i != (nextx, nexty) ) # remove the corner which reached
+                else:
+                    new_corners = state['target_corners']
+
+                new_state = {
+                    'position': (nextx, nexty),
+                    'target_corners': new_corners,
+                }
+
+                successors.append((new_state, action, 1))
 
         self._expanded += 1 # DO NOT CHANGE
         return successors
@@ -403,4 +423,4 @@ class FoodSearchProblem:
             if self.walls[x][y]:
                 return 999999
             cost += 1
-        return cost
\ No newline at end of file
+        return cost