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# Solved board games

A two-player game can be "solved" on several levels.
1. Ultra-weak: In the weakest sense, solving a game means proving whether the first player will win, lose, or draw from the initial position, given perfect play on both sides.
2. Weak: More typically, solving a game means providing an algorithm which secures a win for one player, or a draw for either, against any possible moves by the opponent, from the initial position only.
3. Strong: The strongest sense of solution requires an algorithm which can produce perfect play from any position, i.e. even if mistakes have already been made on one or both sides. For a game with a finite number of positions, this is always possible with a powerful enough computer, by checking all the positions. However, there is the question of finding an efficient algorithm, or an algorithm that works on computers currently available.

## Solved games

• Awari (a game of the Mancala family)
• Solved by Henri Bal and John Romein at the Free University in Amsterdam, Netherlands (2002). Either player can force the game into a draw.
• Connect Four
• Solved by both Victor Allis (1988) and James Allen (1989) independently. First player can force a win.
• Gomoku
• Solved by Victor Allis (1993) First player can force a win.
• Hex
• Completely solved (definition #3) by several computers for board sizes up to 6x6.
• Jing Yang has demonstrated a winning strategy (definition #2) for board sizes 7x7, 8x8 and 9x9. [1]
• John Nash showed that all board sizes are won for the first player (definition #1).
• The discovery of an efficient general algorithm for an NxN board is unlikely as the problem has been shown to be NP-hard.
• Nim
• Completely solved for all starting configurations.
• Nine men's morris
• Solved by Ralph Gasser (1993). Either player can force the game into a draw. [1]
• Pentominoes
• Weakly solved (definition #2) by H. K. Orman. It is a win for the first player.
• Qubic
• Solved by Patashnik (1980).
• Three Men's Morris
• Trivially solvable. Either player can force the game into a draw
• Tic-tac-toe
• Trivially solvable. Either player can force the game into a draw

## Partially solved games

• Checkers
• Endgames up to 8 pieces have been solved. Not all early-game positions have been solved, but almost all midgame positions are solved. Contrary to popular belief, Checkers is not completely solved.
• Chess
• Completely solved (definition #3) by retrospective computer analysis for all 2- to 5-piece endgames, counting the two kings as pieces. Also solved for pawnless 3-3 and most 4-2 endgames.
• Go
• Solved (definition #3) for board sizes up to 4x4. The 5x5 board is partially solved. [1] Humans usually play on a 19x19 board (which has an enormous complexity). Therefore solving the game appears very unlikely. On the other hand, a heuristic algorithmic solution might be achievable in the future. While not mathematically complete, it could give good results in practice, perhaps beating even the best human players.
• Reversi
• solved on a 4x4 and 6x6 board as a second player win.
• mnk-games
• It is trivial to show that the second player can never win. Almost all cases have been solved weakly for k <= 4. Some results are known for k = 5. The games are drawn for k >= 8.