Alpha-Beta Pruning.

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Presentation transcript:

Alpha-Beta Pruning

Re-cap Game Theory Design Game Tree Min-Max Algorithm (aka "Minimax" )  get the value of a node by sending off an accumulator Depth-limited Min-Max Algorithm Design Separation of Concerns

Alpha-Beta Pruning What it does: From root node of a game tree, get the best outcome value of a path How it does the job Key assumption: 2 players …

Child close over Parent Inheritance Inheritance Child close over Parent

Tranverse & Prune AlphaAcc, -1 new AlphaAcc, -Max AlphaAcc, -1 new BetaAcc, Max b <= a? BetaAcc, -1 Prune! new AlphaAcc, -Max B <= a? new AlphaAcc, -Max B <= a? AlphaAcc, 1 B <= a? AlphaAcc, -1 B <= a? B <= a? BetaAcc,1 BetaAcc, -1 new BetaAcc, Max new BetaAcc, Max B <= a? B <= a? …..

Other OO elements AlphaBetaFact

Goals of presentation – till 8 am Understand Alpha-Beta Pruning How the logic of the algorithm drives design of implementation The logic: 1 hr Is MinMax Alpha, Beta inherit max & min accum Need to compare alpha vs beta in the middle of a alpha-beta recursion What needs to express in OO: 0.5 Inheritance done Child closing over parent done