I am fairly new to python and want to play around to the given python code. The

Question

I am fairly new to python and want to play around to the given python code. The instructions say:

How-to:  To use this code, create a new instance of the Minimax object, and pass in your GameTree object. This code should work on any GameTree object that has fields for: 1) child nodes; 2) value. After the Minimax object is instantiated, run the minimax() function.

So now I was wondering how I can test the following input:  ((3,12,8),(2,4,6),(14,5,2))

The output should be 3 as it will be the max value after minimax algorithm is ran.

[Code]

[/EndCode]

class MiniMax: # print utility value of root node (assuming it is max) # print names of all nodes visited during search def __init__(self, game_tree): self.game_tree = game_tree # GameTree self.root = game_tree.root # GameNode self.currentNode = None # GameNode self.successors = [] # List of GameNodes return def minimax(self, node): # first, find the max value best_val = self.max_value(node) # should be root node of tree # second, find the node which HAS that max value # --> means we need to propagate the values back up the # tree as part of our minimax algorithm successors = self.getSuccessors(node) print "MiniMax: Utility Value of Root Node: = " + str(best_val) # find the node with our best move best_move = None for elem in successors: # ---> Need to propagate values up tree for this to work if elem.value == best_val: best_move = elem break # return that best value that we've found return best_move def max_value(self, node): print "MiniMax-->MAX: Visited Node :: " + node.Name if self.isTerminal(node): return self.getUtility(node) infinity = float('inf') max_value = -infinity successors_states = self.getSuccessors(node) for state in successors_states: max_value = max(max_value, self.min_value(state)) return max_value def min_value(self, node): print "MiniMax-->MIN: Visited Node :: " + node.Name if self.isTerminal(node): return self.getUtility(node) infinity = float('inf') min_value = infinity successor_states = self.getSuccessors(node) for state in successor_states: min_value = min(min_value, self.max_value(state)) return min_value # # # UTILITY METHODS # # # # successor states in a game tree are the child nodes... def getSuccessors(self, node): assert node is not None return node.children # return true if the node has NO children (successor states) # return false if the node has children (successor states) def isTerminal(self, node): assert node is not None return len(node.children) == 0 def getUtility(self, node): assert node is not None return node.value

Explanation / Answer

# print utility value of root node (assuming it is max) # print names of all nodes visited during search def __init__(self, game_tree): self.game_tree = game_tree # GameTree self.root = game_tree.root # GameNode self.currentNode = None # GameNode self.successors = [] # List of GameNodes return def minimax(self, node): # first, find the max value best_val = self.max_value(node) # should be root node of tree # second, find the node which HAS that max value # --> means we need to propagate the values back up the # tree as part of our minimax algorithm successors = self.getSuccessors(node) print "MiniMax: Utility Value of Root Node: = " + str(best_val) # find the node with our best move best_move = None for elem in successors: # ---> Need to propagate values up tree for this to work if elem.value == best_val: best_move = elem break # return that best value that we've found return best_move def max_value(self, node): print "MiniMax-->MAX: Visited Node :: " + node.Name if self.isTerminal(node): return self.getUtility(node) infinity = float('inf') max_value = -infinity successors_states = self.getSuccessors(node) for state in successors_states: max_value = max(max_value, self.min_value(state)) return max_value def min_value(self, node): print "MiniMax-->MIN: Visited Node :: " + node.Name if self.isTerminal(node): return self.getUtility(node) infinity = float('inf') min_value = infinity successor_states = self.getSuccessors(node) for state in successor_states: min_value = min(min_value, self.max_value(state)) return min_value # # # UTILITY METHODS # # # # successor states in a game tree are the child nodes... def getSuccessors(self, node): assert node is not None return node.children # return true if the node has NO children (successor states) # return false if the node has children (successor states) def isTerminal(self, node): assert node is not None return len(node.children) == 0 def getUtility(self, node): assert node is not None return node.value

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