Coulom had exchanged ideas with a fellow academic named Bruno Bouzy, who believed that the secret to computer Go might lie in a search algorithm known as Monte Carlo. Rather than having to search every branch of the game tree, Monte Carlo would play out a series of random games from each possible move, and then deduce the value of the move from an analysis of the results.
While Bouzy was unable to make the idea work, Coulom hit upon a novel way of combining the virtues of tree search with the efficiency of Monte Carlo. He christened the new algorithm Monte Carlo Tree Search, or MCTS, and in January of 2006, his program Crazy Stone won its first tournament. He published his landmark concept in a paper that changed Go programs, setting a dividing point for programs before MCTS and those after.
AlphaGo vs Lee Sedol: history in the making