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Perfect Information

Barricade

Alpha-beta + shortest-path heuristic.

2 players2 solversHeuristic
Alpha-BetaHeuristicBest move
Position
Click your pawn's legal destination (green dot) to move, or click a wall slot to place a barricade. Click an existing wall to remove it.
P1 shortest path: 8(10 walls)P2 shortest path: 8(10 walls) P1 to move
Suggestion
Iterative-deepening negamax with alpha-beta and the Glendenning shortest-path heuristic.

Tap Analyse to compute the best move.

Deep dive

How BoardSolve plays Barricade

Barricade-style games (Quoridor, barricade.gg) combine pawn movement and wall placement on a 9×9 board. The branching factor is large but the value of a position is dominated by the shortest-path differential between the two players — a fact first exploited in Lisa Glendenning's 2002 thesis.

Search

BoardSolve performs an iterative-deepening negamax with alpha-beta pruning and a killer-move table. At each leaf the evaluation function is the difference of BFS shortest-path lengths from each player's pawn to its goal row, minus a small term for remaining walls in hand.

Wall-placement moves are filtered: only walls that actually change one player's shortest path by ≥ 1 (or block a tactical pattern) are considered, which prunes the branching factor from ~130 to a few dozen without losing strength in practice.

Legality check

Every candidate wall is validated by re-running BFS for both pawns — Quoridor's hardest rule is that no wall may completely block either player's path to its goal.

References & further reading

  1. Glendenning, L. (2002) . B.Sc. thesis, University of New MexicoIntroduces the shortest-path-difference evaluation BoardSolve uses.
  2. Mertens, P. J. C. (2006) . B.Sc. thesis, Maastricht UniversityEmpirical comparison of evaluation functions and move-ordering heuristics for Quoridor.
  3. Respall, V. M., Brown, J. A. & Aslam, H. (2018) . 19th GAME-ON Conference