Peg Solitaire

Goal of the game

Remove the marbles one by one until only a single marble is left on the board. At Diabolical level, that last marble must finish on the square marked with a golden ring.

How it works

• A marble jumps over a neighbouring one (horizontally or vertically, never diagonally) to land in the empty hole just behind it.
• The jumped marble is captured and rolls into the board's gutter.
• The game stops when no more jumps are possible.
• A sequence of jumps made by the same marble counts as a single move: that is how experts measure themselves.

Controls

• Tap a marble, then the destination hole (the possible destinations light up), or drag the marble.
• Tap an empty hole directly: if only one jump can lead there, it is played.
• Keyboard: arrow keys to move the cursor, Space to pick the marble then the destination.

Levels

• Easy, Medium, Hard: layouts of 8, 13 and 19 marbles created by reverse play (jumps played backwards from a single marble), so they can always be solved; their difficulty is measured over thousands of random games.
• Expert: full board, with a starting hole drawn at random among those that allow finishing with a single marble.
• Diabolical: full board and an imposed finishing square, like the famous central problem of the English board.

About the AI

The solver explores the tree of jumps depth-first, remembering every losing position, identified up to its symmetries (rotations and reflections of the board), and orders the jumps to avoid isolated marbles. Colouring invariants modulo 2 and 3 prune positions that can no longer lead to a single marble. A hint tells you whether you are still on a winning path, and if not, how many jumps to undo.

Records are only recognised without hints or AI help.