Negamax

Negamax search is a slightly variant formulation of minimax search that relies on the zero-sum property of a two-player game.

By definition the value of a position to player A in such a game is the negation of the value to player B. Thus, the player on move looks for a move that maximizes the negation of the value of the position resulting from the move: this successor position must by definition have been valued by the opponent. The reasoning of the previous sentence works regardless of whether A or B is on move. This means that a single computation can be used to value all positions. This is a coding simplification over minimax, which requires that A select the move with the maximum-valued successor while B selects the move with the minimum-valued successor.

Most adversary search engines are coded using some form of negamax search.