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A-Star.py
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A-Star.py
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from collections import deque
class PriorityQueue:
def __init__(self):
self.fn={}
self.nodes={}
def append(self,node):
problem=Problem('Arad','Bucharest')
if node.state not in self.fn.keys():
self.fn[node.state]=int(problem.h(node.state))+node.path_cost
self.nodes[node.state]=node
def pop(self):
# Find state with minmum f-value
state= min(self.fn, key=self.fn.get)
del self.fn[state]
node=self.nodes[state]
del self.nodes[state]
return node
def replace(self,child):
problem=Problem('Arad','Bucharest')
if self.contains(child) and self.fn[child.state]>int(problem.h(child.state))+child.path_cost:
self.fn[child.state]=int(problem.h(child.state))+child.path_cost
self.nodes[child.state]=child
def IsEmpty(self):
return not self.fn
def Clear(self):
self.fn={}
self.nodes={}
def contains(self,node):
return node.state in self.fn.keys()
def __str__(self):
str1 = ' '.join(str(e) for e in self.fn.keys())
return str1
# ______________________________________________________________________________
class Problem(object):
def __init__(self, init_state, goal_state):
self.initial_state = init_state;
self.goal_state = goal_state;
self.state_space = {};
self.state_space['Arad'] = {'GoZerind': 'Zerind', 'GoSibiu' : 'Sibiu', 'GoTimisoara': 'Timisoara'};
self.state_space['Zerind'] = {'GoOradea': 'Oradea', 'GoArad' : 'Arad' };
self.state_space['Oradea'] = {'GoSibiu': 'Sibiu', 'GoZerind': 'Zerind'};
self.state_space['Timisoara'] = {'GoLugoj' : 'Lugoj', 'GoArad' : 'Arad'};
self.state_space['Lugoj'] = {'GoTimisoara' : 'Timisoara', 'GoMehandia' : 'Mehandia'};
self.state_space['Drobeta'] = {'GoMehandia' : 'Mehandia', 'GoCraiova' : 'Craiova'};
self.state_space['Craiova'] = {'GoDrobeta' : 'Drobeta', 'GoRimnicu' : 'Rimnicu Vilcea', 'GoPitesti' : 'Pitesti'};
self.state_space['Rimnicu Vilcea'] = {'GoSibiu' : 'Sibiu', 'GoPitesti' : 'Pitesti', 'GoCraoova' : 'Craiova'};
self.state_space['Sibiu'] = {'GoArad' : 'Arad', 'GoFagaras' : 'Fagaras', 'GoOradea' : 'Oradea', 'GoRimnicu' :
'Rimnicu Vilcea'};
self.state_space['Fagaras'] = {'GoSibiu' : 'Sibiu', 'GoBucharest' : 'Bucharest'};
self.state_space['Pitesti'] = {'GoRimnicu' : 'Rimnicu Vilcea', 'GoCraiova' : 'Craiova', 'GoBucharest' :
'Bucharest'};
self.state_space['Bucharest'] = {'GoFagaras' : 'Fagaras', 'GoPitesti' : 'Pitesti', 'GoGiurgiu' : 'Giurgiu',
'GoUrziceni' : 'Urziceni'};
self.state_space['Giurgiu'] = {'GoBucharest' : 'Bucharest'};
self.state_space['Urziceni'] = {'GoBucharest' : 'Bucharest', 'GoValsui' : 'Valsui', 'GoHirsova' : 'Hirsova'};
self.state_space['Hirsova'] = {'GoEforie' : 'Eforie', 'GoUrziceni' : 'Urziceni'};
self.state_space['Eforie'] = {'GoHirsova' : 'Hirsova'};
self.state_space['Valsui'] = {'GoUrziceni' : 'Urziceni', 'GoIasi' : 'Iasi'};
self.state_space['Iasi'] = {'GoValsui' : 'Valsui', 'GoNeamt' : 'Neamt'};
self.state_space['Neamt'] = {'GoIasi' : 'Iasi'};
self.state_space['Mehandia'] = {'GoLugoj' : 'Lugoj','GoDrobeta' : 'Drobeta'};
self.step_cost = {};
self.step_cost['Arad'] = {'GoZerind': '75', 'GoSibiu': '140', 'GoTimisoara': '118'};
self.step_cost['Zerind'] = {'GoOradea': '71', 'GoArad': '75'};
self.step_cost['Oradea'] = {'GoSibiu': '152', 'GoZerind': '71'};
self.step_cost['Timisoara'] = {'GoLugoj': '111', 'GoArad': '118'};
self.step_cost['Lugoj'] = {'GoTimisoara': '111', 'GoMehandia': '70'};
self.step_cost['Drobeta'] = {'GoMehandia': '75', 'GoCraiova': '120'};
self.step_cost['Craiova'] = {'GoDrobeta': '120', 'GoRimnicu': '146', 'GoPitesti': '138'};
self.step_cost['Rimnicu Vilcea'] = {'GoSibiu': '80', 'GoPitesti': '97', 'GoCraoova': '146'};
self.step_cost['Sibiu'] = {'GoArad': '140', 'GoFagaras': '99', 'GoOradea': '151','GoRimnicu': '80'};
self.step_cost['Mehandia'] = {'GoLugoj' : '70','GoDrobeta' : '75'};
self.step_cost['Fagaras'] = {'GoSibiu': '99', 'GoBucharest': '211'};
self.step_cost['Pitesti'] = {'GoRimnicu': '97', 'GoCraiova': '138', 'GoBucharest': '101'};
self.step_cost['Bucharest'] = {'GoFagaras': '211', 'GoPitesti': '101', 'GoGiurgiu': '90', 'GoUrziceni': '85'};
self.step_cost['Giurgiu'] = {'GoBucharest': '90'};
self.step_cost['Urziceni'] = {'GoBucharest': '85', 'GoValsui': '142', 'GoHirsova': '98'};
self.step_cost['Hirsova'] = {'GoEforie': '86', 'GoUrziceni': '98'};
self.step_cost['Eforie'] = {'GoHirsova': '86'};
self.step_cost['Valsui'] = {'GoUrziceni': '142', 'GoIasi': '92'};
self.step_cost['Iasi'] = {'GoValsui': '92', 'GoNeamt': '87'};
self.step_cost['Neamt'] = {'GoIasi': '87'};
self.heuristics = {};
self.heuristics['Arad'] = 366;
self.heuristics['Zerind'] = 374;
self.heuristics['Oradea'] =380;
self.heuristics['Timisoara'] = 329;
self.heuristics['Lugoj'] = 244;
self.heuristics['Drobeta'] = 242;
self.heuristics['Craiova'] = 160;
self.heuristics['Rimnicu Vilcea'] = 193;
self.heuristics['Sibiu'] = 253;
self.heuristics['Fagaras'] = 176;
self.heuristics['Pitesti'] = 100;
self.heuristics['Bucharest'] = 0;
self.heuristics['Giurgiu'] = 77;
self.heuristics['Urziceni'] = 80;
self.heuristics['Hirsova'] = 151;
self.heuristics['Eforie'] = 161;
self.heuristics['Valsui'] = 199;
self.heuristics['Iasi'] = 226;
self.heuristics['Neamt'] = 234;
self.heuristics['Mehandia'] = 241;
def Actions(self, state):
lst=self.state_space[state].keys()
return lst
def Result(self, state, action):
return self.state_space[state][action]
def Goal_test(self, state):
return state == self.goal_state
def Path_cost(self, state, action):
return self.step_cost[state][action]
def h(self, state):
return self.heuristics[state]
# ______________________________________________________________________________
class Node:
def __init__(self, state, parent=None, action=None, path_cost=0):
"""Create a search tree Node, derived from a parent by an action."""
self.state = state
self.parent = parent
self.action = action
self.path_cost = path_cost
def __repr__(self):
return "<Node {} {} >".format(self.state,self.path_cost)
def __lt__(self, node):
return self.state < node.state
def __eq__(self, other):
return isinstance(other, Node) and self.state == other.state
#-----------------------------------------------------------------------------
def child_node(problem,parent, action):
next_state = problem.Result(parent.state, action)
step_cost= problem.Path_cost(parent.state, action)
next_node = Node(next_state, parent,action, parent.path_cost+int(step_cost))
return next_node
def solution(node):
path_back =[]
while node:
path_back.append(node)
node = node.parent
for n in reversed(path_back):
print (n)
# ______________________________________________________________________________
def Astar(problem):
node=Node(problem.initial_state)
frontier = PriorityQueue()
frontier.append(node)
explored=[]
while True:
if frontier.IsEmpty(): return print('Failure')
node=frontier.pop()
#print(node) uncomment to understand working of algorithm
if problem.Goal_test(node.state): return solution(node)
explored.append(node.state)
for action in problem.Actions(node.state):
child=child_node(problem,node,action)
if child.state not in explored and not frontier.contains(child):
frontier.append(child)
elif frontier.contains(child):
frontier.replace(child)
# ____________________________________________________________________________
# Program main part
problem=Problem('Arad','Bucharest')
Astar(problem)