def UCS(initial_state):
'''Uniform Cost Search. This is the actual algorithm.'''
global g, COUNT, BACKLINKS, MAX_OPEN_LENGTH, CLOSED, TOTAL_COST
CLOSED = []
BACKLINKS[initial_state] = None
# The "Step" comments below help relate UCS's implementation to
# those of Depth-First Search and Breadth-First Search.
# STEP 1a. Put the start state on a priority queue called OPEN
OPEN = PriorityQueue()
OPEN.insert(initial_state, 0)
# STEP 1b. Assign g=0 to the start state.
g[initial_state] = 0.0
cost_so_far = g[initial_state]
# STEP 2. If OPEN is empty, output “DONE” and stop.
# while False: # ***STUDENTS CHANGE THIS CONDITION***
while OPEN != []:
# LEAVE THE FOLLOWING CODE IN PLACE TO INSTRUMENT AND/OR DEBUG YOUR IMPLEMENTATION
if VERBOSE: report(OPEN, CLOSED, COUNT)
if len(OPEN) > MAX_OPEN_LENGTH: MAX_OPEN_LENGTH = len(OPEN)
# STEP 3. Select the state on OPEN having lowest priority value and call it S.
# Delete S from OPEN.
# Put S on CLOSED.
# If S is a goal state, output its description
(S, P) = OPEN.delete_min()
cost_so_far += P
g[S] = cost_so_far
# print(f"currently at {S.name} ")
# print(f"cost from {initial_state.name} to {S.name} = {cost_so_far}")
# print("In Step 3, returned from OPEN.delete_min with results (S,P)= \n", (str(S), P))
# print("BACKLINKS = ")
# for state in BACKLINKS.keys():
# print("parent = " + str(BACKLINKS.get(state)) + ", child = " + str(state))
CLOSED.append(S)
if Problem.GOAL_TEST(S):
print("\n" + Problem.GOAL_MESSAGE_FUNCTION(S) + "\n")
# handling backtracing
SOLUTION_PATH = [str(s)
for s in backtrace(S)] # should return a list
print(f"Solution path = {SOLUTION_PATH}")
print('Length of solution path found: ' +
str(len(SOLUTION_PATH) - 1) + ' edges')
# handling total cost
TOTAL_COST = g[S]
print("TOTAL_COST = " + str(TOTAL_COST))
return
COUNT += 1
print("EXPANDING = ", S.name)
# STEP 4. Generate each successor of S
# and if it is already on CLOSED, delete the new instance.
successors = []
for op in Problem.OPERATORS:
if op.precond(S):
new_state = op.state_transf(S)
priority = cost_so_far + new_state.edge_distance(S)
# if successor is not on CLOSED and OPEN, add to successors
if not (new_state in CLOSED) and not (new_state in OPEN):
successors.append((new_state, priority))
BACKLINKS[new_state] = S
else:
if new_state in OPEN:
if OPEN[new_state] > priority:
OPEN.__delitem__(new_state)
OPEN.insert(new_state, priority)
# print(f"PREVIOUS BACKLINK FOR {new_state} = {BACKLINKS[new_state].name}")
BACKLINKS[new_state] = S
# print(f"UPDATING BACKLINK FOR {new_state} = {BACKLINKS[new_state].name}")
# print(f"UPDATING PRIORITY FOR {new_state} = {OPEN[new_state]}")
elif new_state in CLOSED:
# If sj occurs on CLOSED, and its new distance is smaller than its old distance,
# then it is taken off of CLOSED, put back on OPEN, but with the new, smaller distance.
for item in CLOSED:
if item == new_state:
old_distance = g[item]
if old_distance > priority:
CLOSED.remove(item)
# print(f"STATE {new_state} IS ON CLOSED.")
# print(f"OLD DISTANCE = {old_distance} vs NEW DISTANCE = {new_distance}")
# print(f"CURRENT CLOSED = {str(CLOSED)}")
OPEN.insert(new_state, priority)
BACKLINKS[new_state] = S
for (s, p) in successors:
OPEN.insert(s, p)
print_state_queue("OPEN", OPEN)
# print("CLOSED: [ ", end="")
# for state in CLOSED:
# print(state.name, end=" ")
# print("]")
cost_so_far -= P # reset cost_so_far to current shortest path
# STEP 6. Go to Step 2.
return None # No more states on OPEN, and no goal reached.
def AStar(initial_state):
'''AStar Search. This is the actual algorithm.'''
global g, COUNT, BACKLINKS, MAX_OPEN_LENGTH, CLOSED, TOTAL_COST
##CLOSED = []
CLOSED = My_Priority_Queue()
BACKLINKS[initial_state] = None
# The "Step" comments below help relate AStar's implementation to
# those of Depth-First Search and Breadth-First Search.
# STEP 1a. Put the start state on a priority queue called OPEN
OPEN = My_Priority_Queue()
OPEN.insert(initial_state, 0)
# STEP 1b. Assign g=0 to the start state.
g[initial_state]=0.0
# STEP 2. If OPEN is empty, output “DONE” and stop.
while len(OPEN)>0:
if VERBOSE: report(OPEN, CLOSED, COUNT)
if len(OPEN)>MAX_OPEN_LENGTH: MAX_OPEN_LENGTH = len(OPEN)
# STEP 3. Select the state on OPEN having lowest priority value and call it S.
# Delete S from OPEN.
# Put S on CLOSED.
# If S is a goal state, output its description
(S,P) = OPEN.delete_min()
#print("In Step 3, returned from OPEN.delete_min with results (S,P)= ", (str(S), P))
#####CLOSED.append(S)
#print("current S =" + str(S))
#if(CLOSED.__contains__(S)):
# CLOSED.__delitem__(S)
CLOSED.insert(S,P)
if Problem.GOAL_TEST(S):
print(Problem.GOAL_MESSAGE_FUNCTION(S))
path = backtrace(S)
print('Length of solution path found: '+str(len(path)-1)+' edges')
TOTAL_COST = g[S]
print('Total cost of solution path found: '+str(TOTAL_COST))
return path
COUNT += 1
# STEP 4. Generate each successors of S and delete
# if it is already on CLOSED, delete the new instance.
gs = g[S] # Save the cost of getting to S in a variable.
for op in Problem.OPERATORS:
if op.precond(S):
new_state = op.state_transf(S)
edge_cost = S.edge_distance(new_state)
new_gs = gs + edge_cost #dist of s + sucessor
new_hs = h(new_state) #heuristic vallue of sucessor
new_fs = new_gs + new_hs #priortiy value
if (new_state in CLOSED):
prev_new_state_fs = CLOSED[new_state] #return the P of state in CLOSED list
# new state has lower cost
if (new_fs < prev_new_state_fs):
CLOSED.__delitem__(new_state)
OPEN.insert(new_state, new_fs)
# new state has greater cost so delete
else:
del new_state
continue
# If new_state already exists on OPEN:
# If its new priority is less than its old priority,
# update its priority on OPEN, and set its BACKLINK to S.
# Else: forget out this new state object... delete it.
elif (new_state in OPEN):
P = OPEN[new_state] #returns priority
# new state has lower cost
if (new_fs < P):
#print("New priority value is lower, so del older one")
OPEN.__delitem__(new_state)
OPEN.insert(new_state, new_fs)
# new state has greater cost
else:
#print("Older one is better, so del new_state")
del new_state
continue
#print("new_state was not on OPEN at all, so just put it on.")
else:
OPEN.insert(new_state, new_fs)
BACKLINKS[new_state] = S
g[new_state] = new_gs
#print_state_queue("OPEN", OPEN)
#print_state_queue("CLOSED", CLOSED)
#print("\n")
# STEP 6. Go to Step 2.
return None # No more states on OPEN, and no goal reached.
def UCS(initial_state):
'''Uniform Cost Search. This is the actual algorithm.'''
global g, COUNT, BACKLINKS, MAX_OPEN_LENGTH, CLOSED, TOTAL_COST
CLOSED = []
BACKLINKS[initial_state] = None
# The "Step" comments below help relate UCS's implementation to
# those of Depth-First Search and Breadth-First Search.
# STEP 1a. Put the start state on a priority queue called OPEN
OPEN = My_Priority_Queue()
OPEN.insert(initial_state, 0)
# STEP 1b. Assign g=0 to the start state.
g[initial_state] = 0.0
# STEP 2. If OPEN is empty, output “DONE” and stop.
while len(OPEN) > 0:
if VERBOSE: report(OPEN, CLOSED, COUNT)
if len(OPEN) > MAX_OPEN_LENGTH: MAX_OPEN_LENGTH = len(OPEN)
# STEP 3. Select the state on OPEN having lowest priority value and call it S.
# Delete S from OPEN.
# Put S on CLOSED.
# If S is a goal state, output its description
(S, P) = OPEN.delete_min()
# print("In Step 3, returned from OPEN.delete_min with results (S,P)= ", (str(S), P))
CLOSED.append(S)
if Problem.GOAL_TEST(S):
print(Problem.GOAL_MESSAGE_FUNCTION(S))
path = backtrace(S)
print('Length of solution path found: ' + str(len(path) - 1) +
' edges')
TOTAL_COST = g[S]
print('Total cost of solution path found: ' + str(TOTAL_COST))
return path
COUNT += 1
# STEP 4. Generate each successors of S and delete
# and if it is already on CLOSED, delete the new instance.
gs = g[S] # Save the cost of getting to S in a variable.
for op in Problem.OPERATORS:
if op.precond(S):
new_state = op.state_transf(S)
if (new_state in CLOSED):
# print("Already have this state, in CLOSED. del ...")
del new_state
continue
edge_cost = S.edge_distance(new_state)
new_g = gs + edge_cost
# If new_state already exists on OPEN:
# If its new priority is less than its old priority,
# update its priority on OPEN, and set its BACKLINK to S.
# Else: forget out this new state object... delete it.
if new_state in OPEN:
# print("new_state is in OPEN already, so...")
P = OPEN[new_state]
if new_g < P:
# print("New priority value is lower, so del older one")
del OPEN[new_state]
OPEN.insert(new_state, new_g)
else:
# print("Older one is better, so del new_state")
del new_state
continue
else:
# print("new_state was not on OPEN at all, so just put it on.")
OPEN.insert(new_state, new_g)
BACKLINKS[new_state] = S
g[new_state] = new_g
# print_state_queue("OPEN", OPEN)
# STEP 6. Go to Step 2.
return None # No more states on OPEN, and no goal reached.
def UCS(initial_state):
'''Uniform Cost Search. This is the actual algorithm.'''
global g, COUNT, BACKLINKS, MAX_OPEN_LENGTH, CLOSED, TOTAL_COST
CLOSED = []
BACKLINKS[initial_state] = None
# The "Step" comments below help relate UCS's implementation to
# those of Depth-First Search and Breadth-First Search.
# STEP 1a. Put the start state on a priority queue called OPEN
OPEN = My_Priority_Queue()
OPEN.insert(initial_state, 0)
# STEP 1b. Assign g=0 to the start state.
g[initial_state] = 0.0
# STEP 2. If OPEN is empty, output “DONE” and stop.
while OPEN != []: # ***STUDENTS CHANGE THIS CONDITION***
# LEAVE THE FOLLOWING CODE IN PLACE TO INSTRUMENT AND/OR DEBUG YOUR IMPLEMENTATION
if VERBOSE: report(OPEN, CLOSED, COUNT)
if len(OPEN) > MAX_OPEN_LENGTH: MAX_OPEN_LENGTH = len(OPEN)
# STEP 3. Select the state on OPEN having lowest priority value and call it S.
# Delete S from OPEN.
# Put S on CLOSED.
# If S is a goal state, output its description
(S, P) = OPEN.delete_min()
#print("In Step 3, returned from OPEN.delete_min with results (S,P)= ", (str(S), P))
distance = P
CLOSED.append(S)
if Problem.GOAL_TEST(S):
print(Problem.GOAL_MESSAGE_FUNCTION(S))
path = backtrace(S)
print('Length of solution path found: ' + str(len(path) - 1) +
' edges')
print('The distance between start state and destination is:',
str(distance))
return # ***STUDENTS CHANGE THE BODY OF THIS IF.***
#HANDLE THE BACKTRACING, RECORDING THE SOLUTION AND TOTAL COST,
# AND RETURN THE SOLUTION PATH, TOO.
COUNT += 1
# STEP 4. Generate each successor of S
# and if it is already on CLOSED, delete the new instance.
i = 0
while True: #find out the # of neighbors(i) for S
if not S.ith_neighbor_exists(i):
for j in range(i):
ne = S.move(j) #get neighbor name
P = S.edge_distance(ne) #get distance to neighbor
if ne not in CLOSED and ne not in OPEN: #make sure neighbor not in CLOSED
BACKLINKS[ne] = S
g[ne] = g[S] + P
OPEN.insert(ne, g[ne])
break
i += 1
#find links of s, and add them to open.
#add backtrace
# ***STUDENTS IMPLEMENT THE GENERATION AND HANDLING OF SUCCESSORS HERE,
# USING THE GIVEN PRIORITY QUEUE FOR THE OPEN LIST, AND
# DETERMINING THE SHORTEST DISTANCE KNOWN SO FAR FROM THE INITIAL STATE TO
# EACH SUCCESSOR.***
# STEP 6. Go to Step 2.
return None # No more states on OPEN, and no goal reached.