Fix the implementation

A number of things wrong with the quickie code initially committed,
chiefly not mutating the caller's copy of the board when that was the
intention. This commit fixes this and produces a working solver for all
boards that can be solved without exploration/uncertainty.

1 files changed, 17 insertions, 0 deletions

diff --git a/TODO b/TODO
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+The solver can only solve when at least one cell can be solved with certainty
+at each step of the process until repeating this eventually results in a solved
+board.
+The next step here is to allow exploration/trail of possible solutions.
+Presumably, would want to keep a copy of the board just before each "guess"
+that's taken to be able to easily roll back if failure.
+
+This would probably work really nicely as a recursive call:
+
+	board = get_fresh_board(board)
+	solve_all_certainties(board)
+	for each possible board as cand_board:
+		solution = solve_all_certainties(cand_board)
+		if complete(solution)
+			success
+	/* we should have solution presuming board was solvable */
+