研究这个pacman程序中关于深度优先算法中的3个问题

Question

pacman 程序所在网址: https://blog.csdn.net/junruitian/article/details/79055577

这个是比较热门的python的练习 pacman.
用到的是深度优先算法。

所有的问题都是关于这个深度优先算法的这一小部分
问题: 1.

 fringe.push((problem.getStartState(), []))# (problem.getStartState(), []) 为什么里面是这么一个元组？ 这个problem不是对象，那到底是什么？如果是抽象类，为什么这里写problem

2:

    # 当前节点
        cur_node, actions = fringe.pop() # 为什么返回的是两个值: cur_node, actions

3.

 util.raiseNotDefined()# 这个语句的目的是什么呢？

下面是Stack类

class Stack:
    "A container with a last-in-first-out (LIFO) queuing policy."
    def __init__(self):
        self.list = []

    def push(self,item):
        "Push 'item' onto the stack"
        self.list.append(item)

    def pop(self):
        "Pop the most recently pushed item from the stack"
        return self.list.pop()

    def isEmpty(self):
        "Returns true if the stack is empty"
        return len(self.list) == 0

下面是search文件和深度优先算法

# search.py
# ---------
# Licensing Information:  You are free to use or extend these projects for
# educational purposes provided that (1) you do not distribute or publish
# solutions, (2) you retain this notice, and (3) you provide clear
# attribution to UC Berkeley, including a link to http://ai.berkeley.edu.
# 
# Attribution Information: The Pacman AI projects were developed at UC Berkeley.
# The core projects and autograders were primarily created by John DeNero
# ([e-mail]) and Dan Klein ([e-mail]).
# Student side autograding was added by Brad Miller, Nick Hay, and
# Pieter Abbeel ([e-mail]).


"""
In search.py, you will implement generic search algorithms which are called by
Pacman agents (in searchAgents.py).
"""

import util

class SearchProblem:
    """
    This class outlines the structure of a search problem, but doesn't implement
    any of the methods (in object-oriented terminology: an abstract class).

    You do not need to change anything in this class, ever.
    """

    def getStartState(self):
        """
        Returns the start state for the search problem.
        """
        util.raiseNotDefined()

    def isGoalState(self, state):
        """
          state: Search state

        Returns True if and only if the state is a valid goal state.
        """
        util.raiseNotDefined()

    def getSuccessors(self, state):
        """
          state: Search state

        For a given state, this should return a list of triples, (successor,
        action, stepCost), where 'successor' is a successor to the current
        state, 'action' is the action required to get there, and 'stepCost' is
        the incremental cost of expanding to that successor.
        """
        util.raiseNotDefined()

    def getCostOfActions(self, actions):
        """
         actions: A list of actions to take

        This method returns the total cost of a particular sequence of actions.
        The sequence must be composed of legal moves.
        """
        util.raiseNotDefined()


def tinyMazeSearch(problem):
    """
    Returns a sequence of moves that solves tinyMaze.  For any other maze, the
    sequence of moves will be incorrect, so only use this for tinyMaze.
    """
    from game import Directions
    s = Directions.SOUTH
    w = Directions.WEST
    return  [s, s, w, s, w, w, s, w]

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 ***"
    from util import Stack
    from game import Directions


    fringe = Stack()
    closed = []


    fringe.push((problem.getStartState(), []))# (problem.getStartState(), []) 为什么里面是这么一个元组？ 这个problem不是对象，那到底是什么？
    print("Start:", problem.getStartState())

    # 如果候选不为空，则循环搜索
    while not fringe.isEmpty():

        # 当前节点
        cur_node, actions = fringe.pop() # 为什么返回的是两个值: cur_node, actions

        # 如果当前节点到达目标位置
        if problem.isGoalState(cur_node):
            return actions

        if cur_node not in closed:
            expand = problem.getSuccessors(cur_node)
            closed.append(cur_node)
            for location, direction, cost in expand:
                if (location not in closed):
                    fringe.push((location, actions + [direction]))

    util.raiseNotDefined()# 这个语句的目的是什么呢？

Answer 1

https://blog.csdn.net/yingGe_0110/article/details/72102209