ift7025-tp1/search/search.py

# 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
# (denero@cs.berkeley.edu) and Dan Klein (klein@cs.berkeley.edu).
# Student side autograding was added by Brad Miller, Nick Hay, and
# Pieter Abbeel (pabbeel@cs.berkeley.edu).


"""
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 ***"
    maPile = util.Stack()
    maListeFermee = []
    # Verifier si le depart est un but
    if problem.isGoalState(problem.getStartState()):
        return []
    # Mettre le premier noeud et un chemin vide dans la pile
    maPile.push((problem.getStartState(),list()))
    # Rechercher tant que la pile n'est pas vide
    while (not maPile.isEmpty()):
        # Extraire le noeud courant
        noeudCourant, listeDirections = maPile.pop()
        # print "Noeud courant: ", noeudCourant
        # La marquer comme visite
        maListeFermee.append(noeudCourant)
        # Verifier si c'est un but
        if(problem.isGoalState(noeudCourant)):
            # print "Nous avons atteint le but !"
            return listeDirections
        # Effectuer la recherche de successeurs
        for s in problem.getSuccessors(noeudCourant):
            # Decomposer le tuple pour faciliter la lecture
            succNoeudCourant, succDirection, succCost = s
            # Verifier si le noeud n'est pas deja visite et n'est pas dans la pile
            if (succNoeudCourant not in maListeFermee):
                # Dans ce cas, ajouter le noeud et le chemin pour s'y rendre a la pile
                # print "Ajout du noeud a la pile: ", succNoeudCourant
                maPile.push((succNoeudCourant,listeDirections+[succDirection]))
    print "pas de solution"
    util.raiseNotDefined()
    
def breadthFirstSearch(problem):
    """Search the shallowest nodes in the search tree first."""
    "*** YOUR CODE HERE ***"
    maFile = util.Queue()
    maListeFermee = []
    # Verifier si le depart est un but
    if problem.isGoalState(problem.getStartState()):
        return []
    # Mettre le premier noeud et un chemin vide dans la file
    maFile.push((problem.getStartState(),list()))
    while (not maFile.isEmpty()):
        # Extraire le noeud courant
        noeudCourant, listeDirections = maFile.pop()
        print "Noeud courant: ", noeudCourant
        # La marquer comme visite
        maListeFermee.append(noeudCourant)
        # Verifier si c'est un but
        if(problem.isGoalState(noeudCourant)):
            print "Nous avons atteint le but !"
            return listeDirections
        # Effectuer la recherche de successeurs
        for s in problem.getSuccessors(noeudCourant):
            # Decomposer le tuple pour faciliter la lecture
            succNoeudCourant, succDirection, succCost = s
            # Verifier si le noeud n'est pas deja visite et n'est pas dans la file
            if (succNoeudCourant not in maListeFermee+[i[0] for i in maFile.list]):
                # Dans ce cas, ajouter le noeud et le chemin pour s'y rendre a la file
                print "Ajout du noeud a la file: ", succNoeudCourant
                maFile.push((succNoeudCourant,listeDirections+[succDirection]))
    print "pas de solution"
    util.raiseNotDefined()

def uniformCostSearch(problem):
    """Search the node of least total cost first."""
    "*** YOUR CODE HERE ***"
    util.raiseNotDefined()

def nullHeuristic(state, problem=None):
    """
    A heuristic function estimates the cost from the current state to the nearest
    goal in the provided SearchProblem.  This heuristic is trivial.
    """
    return 0

def aStarSearch(problem, heuristic=nullHeuristic):
    """Search the node that has the lowest combined cost and heuristic first."""
    "*** YOUR CODE HERE ***"
    util.raiseNotDefined()


# Abbreviations
bfs = breadthFirstSearch
dfs = depthFirstSearch
astar = aStarSearch
ucs = uniformCostSearch