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tracking/ghostAgents.py

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+# ghostAgents.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).
+
+
+from game import Agent
+from game import Actions
+from game import Directions
+import random
+from util import manhattanDistance
+import util
+
+class GhostAgent( Agent ):
+    def __init__( self, index ):
+        self.index = index
+
+    def getAction( self, state ):
+        dist = self.getDistribution(state)
+        if len(dist) == 0:
+            return Directions.STOP
+        else:
+            return util.chooseFromDistribution( dist )
+
+    def getDistribution(self, state):
+        "Returns a Counter encoding a distribution over actions from the provided state."
+        util.raiseNotDefined()
+
+class RandomGhost( GhostAgent ):
+    "A ghost that chooses a legal action uniformly at random."
+    def getDistribution( self, state ):
+        dist = util.Counter()
+        for a in state.getLegalActions( self.index ): dist[a] = 1.0
+        dist.normalize()
+        return dist
+
+class DirectionalGhost( GhostAgent ):
+    "A ghost that prefers to rush Pacman, or flee when scared."
+    def __init__( self, index, prob_attack=0.8, prob_scaredFlee=0.8 ):
+        self.index = index
+        self.prob_attack = prob_attack
+        self.prob_scaredFlee = prob_scaredFlee
+
+    def getDistribution( self, state ):
+        # Read variables from state
+        ghostState = state.getGhostState( self.index )
+        legalActions = state.getLegalActions( self.index )
+        pos = state.getGhostPosition( self.index )
+        isScared = ghostState.scaredTimer > 0
+
+        speed = 1
+        if isScared: speed = 0.5
+
+        actionVectors = [Actions.directionToVector( a, speed ) for a in legalActions]
+        newPositions = [( pos[0]+a[0], pos[1]+a[1] ) for a in actionVectors]
+        pacmanPosition = state.getPacmanPosition()
+
+        # Select best actions given the state
+        distancesToPacman = [manhattanDistance( pos, pacmanPosition ) for pos in newPositions]
+        if isScared:
+            bestScore = max( distancesToPacman )
+            bestProb = self.prob_scaredFlee
+        else:
+            bestScore = min( distancesToPacman )
+            bestProb = self.prob_attack
+        bestActions = [action for action, distance in zip( legalActions, distancesToPacman ) if distance == bestScore]
+
+        # Construct distribution
+        dist = util.Counter()
+        for a in bestActions: dist[a] = bestProb / len(bestActions)
+        for a in legalActions: dist[a] += ( 1-bestProb ) / len(legalActions)
+        dist.normalize()
+        return dist