A solver for the game of Onoro, invented by a friend's uncle.
The game of Onoro is a two-player perfect-information competitive game played on an unmarked flat surface. Each player has 8 pawns (from chess), the first player has black pawns and the second has white.
The goal of the game is to have four pawns in a row. The first player to do so wins. Additionally, if a player has no legal moves, they lose.
The game starts by placing three pawns in a triangle shape, with two black pawns and one white pawn.
Then, players alternate placing pawns, starting with the white player. The rules for placing pawns are:
- Each pawn placed must touch at least two existing pawns. This will force all pawns to align to an infinite hexagonal grid.
Here are the possible moves white can make as their first move:
Since each player has 8 pawns, they will eventually run out of pawns to place. After both players have placed all of their pawns, phase 2 of the game starts.
In phase 2, instead of placing pawns, players may move one of their pawns somewhere else. The following additional constraints are applied:
- After moving the pawn, no pawn may be left connected to only one pawn.
- After moving the pawn, all pawns must form one contiguously connected group. I.e., you may not split the board into two separate groups.
Note that when moving a pawn, these rules may temporarily be violated. As long as the rules are satisfied after the moved pawn is placed, the move is legal.
Assume this is the current board state, and it's black's turn. All pawns have been placed, so it's phase 2.
Here's an example of a legal move black could make, moving the grayed out pawn.
Here's an example of an illegal move. The red pawn can't be moved to where the grayed-out pawn is because it would leave the pawn to the left of it only connected to one other pawn.
Here is a legal move where that same pawn is moved. This is legal because the pawn that would be stranded otherwise is connected to two pawns after the moved pawn is placed.
