def best_friend_search():
open_nodes = []
closed = []
map_obj = Map_Obj(task=4)
endpos = map_obj.get_goal_pos()
start = Node(None, map_obj.get_start_pos(), endpos, 0)
start.g = 0
open_nodes.insert(0, start)
i = 0
while True:
current = open_nodes.pop(0)
if current.pos == endpos:
print("Finished after {} iterations".format(i))
endnode = current
while current.parent is not None:
map_obj.save_frame(i)
print(current.pos)
current = current.parent
map_obj.set_cell_value(current.pos, 'p')
i += 1
map_obj.save_frame(i)
return endnode, map_obj
for pos in current.get_adjacent():
if pos in [node.pos for node in closed]:
continue
if map_obj.get_cell_value(pos) == -1:
continue
cost = map_obj.get_cell_value(pos)
if pos in [node.pos for node in open_nodes]:
for node in open_nodes:
if node.pos == pos:
node.propogate(current)
break
continue
neighbour = Node(current, pos, endpos, current.g + cost)
current.children.append(neighbour)
priority_insert(open_nodes, neighbour)
map_obj.set_cell_value(pos, 'o')
closed.append(current)
map_obj.set_cell_value(current.pos, 0)
if len(open_nodes) == 0:
print("No path found")
return None, map_obj
#if not i%10:
map_obj.save_frame(i)
i += 1
class BestSearchFirst:
def __init__(self, task=1):
self.state_dictionary = {}
self.open = [
] # Sorted by ascending f values, nodes with lot of promise popped early, contains unexpanded nodes
self.closed = [] # no order, contains expanded nodes
self.map = Map_Obj(task) # the map
# creates a new state with coordinates of the goal position from map
self.goal = State(tuple(self.map.get_goal_pos()))
# creates a new state as current state with the coordinates of the start position from map
self.current_state = State(tuple(self.map.get_start_pos()))
self.root_node = Node(self.current_state) # root of the search tree
self.root_node.g = 0
self.heuretic_evaluation(self.root_node)
# all of the f, g, h variables are taken from the appendix added to the task.
self.root_node.f = self.root_node.g + self.root_node.h
# adding the root node to the open list
self.open.append(self.root_node)
self.solution_node = None # Hopefully the goal
def arc_cost(self, p, c):
""" This calculates the arc cost between two nodes (parent and child) using the cost of the child node (the one you are moving to)"""
return self.map.get_cell_value(c.state.coordinates)
def propagate_path_improvements(self, p):
""" Goes through the children of a parent node and updates the cost of
going to the child from the parent if it less than the current cost of going to the child.
This is done recursively """
for c in p.childs:
if p.g + self.arc_cost(p, c) < c.g:
c.parent = p
c.g = p.g + self.arc_cost(p, c)
c.f = c.g + c.h
self.propagate_path_improvements(c)
def agenda_loop(self):
""" Agenda loop """
it = 0
solution = False
while not solution:
it += 1
if not self.open:
# in these tasks with obvious solutions something must be wrong with the implementation
print("Something definitely went wrong!")
return False
x = self.open.pop()
self.closed.append(x)
solution_state = None
if self.check_solution(x):
solution = True
self.solution_node = x
else:
# generating the successor nodes, expanding x
successors = self.generate_successor_nodes(x)
for s in successors: # go through each of these children
in_open = False
in_closed = False
if s in self.open:
in_open = True
s_star = self.open[self.open.index(s)]
if s.state == s_star.state:
s = s_star
elif s in self.closed:
in_closed = True
s_star = self.closed[self.closed.index(s)]
if s.state == s_star.state:
s = s_star
# s is a child of x even though x might not be the best parent
x.childs.append(s)
if not in_open and not in_closed:
# attach the new succesor (it just got explored) with parent x
self.attach_and_eval(s, x)
self.open.append(s) # we will expand this node later
self.open = sorted(self.open,
key=lambda val: val.f,
reverse=True)
# sorting open list in descending based on f value, pop function takes from the back of the list
elif x.g + self.arc_cost(
x, s) < s.g: # found cheaper path to s
# attaches s to a new parent x
self.attach_and_eval(s, x)
if in_closed:
# propagate the improved path to s through all of s children (and their children)
self.propagate_path_improvements(s)
return solution, solution_state
def attach_and_eval(self, c, p):
""" Simply attaches a child node to a node that is now considered its best parent (so far) """
c.parent = p
c.g = p.g + self.arc_cost(p, c)
self.heuretic_evaluation(c)
c.f = c.g + c.h
# This should be changed, need to have a dictionary from coordinates to State
def generate_successor_nodes(self, node):
""" Given a node in the search tree this generates all possible succesor states to the node's state """
directions = [
(1, 0), (-1, 0), (0, 1), (0, -1)
] # directions you are allowed to move in (up, right, left, down)
successor_nodes = [] # all the successors
for i in directions:
x = node.state.coordinates[0] + i[0]
y = node.state.coordinates[1] + i[1]
if tuple((x, y)) in self.state_dictionary:
successor_nodes.append(self.state_dictionary.get(tuple(
(x, y))))
else:
value = self.map.get_cell_value((x, y))
if value != -1: # if it isn't a wall we will add the new node and state to the successors
state = State((x, y))
child = Node(state)
self.state_dictionary[tuple((x, y))] = child
self.heuretic_evaluation(child)
child.g = node.g + self.arc_cost(node, child)
child.f = child.g + child.h
successor_nodes.append(child)
return successor_nodes
def heuretic_evaluation(self, node):
""" Gives a heuretic evaluation of the distance to the goal using manhattan distance """
heuretic = abs(self.goal.coordinates[0] - node.state.coordinates[0]
) + abs(self.goal.coordinates[1] -
node.state.coordinates[1])
node.h = heuretic
return heuretic
def check_solution(self, node):
""" Compares the state of the nodes to the goal state (by comparing coordinates) """
return node.state == self.goal
def print_solution(self):
""" Finds the given solution path by going through the parent of the solution node and going backwards to the root node, then shows the solution using the map """
child = self.solution_node
parent = self.solution_node.parent
solution_list = [self.solution_node.state.coordinates]
while parent != None:
solution_list.append(parent.state.coordinates)
child = parent
parent = child.parent
self.map.show_solution(solution_list)