def depthFirstSearch(problem):
"""
Search the deepest nodes in the search tree first.
Your search algorithm needs to return a list of actions that reaches the
goal. Make sure to implement a graph search algorithm.
To get started, you might want to try some of these simple commands to
understand the search problem that is being passed in:
print "Start:", problem.getStartState()
print "Is the start a goal?", problem.isGoalState(problem.getStartState())
print "Start's successors:", problem.getSuccessors(problem.getStartState())
"""
"*** YOUR CODE HERE ***"
node = Node(problem.getStartState())
if problem.isGoalState(problem.getStartState()): return node.solution()
frontier = util.Stack()
frontier.push(node)
explored = set()
while not frontier.isEmpty():
node = frontier.pop()
if problem.isGoalState(node.state): return node.solution()
explored.add(node.state)
for child in node.expand(problem):
if child.state not in explored:
frontier.push(child)
return None
def bestFirstSearch(problem, heuristic=nullHeuristic):
node = Node(problem.getStartState())
if problem.isGoalState(problem.getStartState()): return node.solution()
frontier = util.PriorityQueue()
frontier.update(node, heuristic(node.state, problem))
explored = set()
while not frontier.isEmpty():
node = frontier.pop()
if problem.isGoalState(node.state): return node.solution()
explored.add(node.state)
for child in node.expand(problem):
if (child.state not in explored) and (child not in frontier.heap):
frontier.update(child, heuristic(child.state, problem))
return None
def aStarSearch(problem, heuristic=nullHeuristic):
"""Search the node that has the lowest combined cost and heuristic first."""
"*** YOUR CODE HERE ***"
node = Node(problem.getStartState())
if problem.isGoalState(problem.getStartState()): return node.solution()
frontier = util.PriorityQueue()
frontier.update(node, node.path_cost + heuristic(node.state, problem))
explored = set()
while not frontier.isEmpty():
node = frontier.pop()
if problem.isGoalState(node.state): return node.solution()
explored.add(node.state)
for child in node.expand(problem):
if (child.state not in explored) and (child not in frontier.heap):
frontier.update(
child, child.path_cost + heuristic(child.state, problem))
return None
def breadthFirstSearch(problem):
"""Search the shallowest nodes in the search tree first."""
"*** YOUR CODE HERE ***"
node = Node(problem.getStartState())
if problem.isGoalState(problem.getStartState()): return node.solution()
frontier = util.Queue()
frontier.push(node)
explored = set()
while not frontier.isEmpty():
node = frontier.pop()
if problem.isGoalState(node.state): return node.solution()
explored.add(node.state)
for child in node.expand(problem):
if (child.state not in explored) and (child.state
not in frontier.list):
if problem.isGoalState(child.state): return child.solution()
frontier.push(child)
return None
