uqac-ia-sudoku-csp/uqac-ia-sudoku-csp/Solver/BacktrackSearch.cs

using System;
using System.Collections.Generic;
using uqac_ia_sudoku_csp.Interfaces;
using uqac_ia_sudoku_csp.Solver.Constraints;

namespace uqac_ia_sudoku_csp.Solver
{
    public class BacktrackSearch : ISolver
    {
        private readonly INextCellChooser _nextCellChooser;
        private readonly INextNumberChooser _nextNumberChooser;
        protected IList<IConstraint> Constraints;

        public BacktrackSearch(INextCellChooser nextCellChooser, INextNumberChooser nextNumberChooser)
        {
            _nextCellChooser = nextCellChooser;
            _nextNumberChooser = nextNumberChooser;
            Constraints = new List<IConstraint>
            {
                new LineContraint(),
                new ColumnConstraint(),
                new BlockConstraint()
            };
        }

        public SolverResult Resolve(Board board)
        {
            var result = new SolverResult();
            var start = DateTime.Now;
            result.Success = RecursiveResolve(board, result);
            var end = DateTime.Now;
            result.Elapsed = end - start;
            return result;
        }

        protected bool RecursiveResolve(Board board, SolverResult result)
        {
            if (board.IsComplete())
            {
                return true;
            }
            int x, y;
            _nextCellChooser.SelectVariable(board, out x, out y, Constraints);
            if (x != -1 && y != -1)
            {
                foreach (var value in _nextNumberChooser.ChooseNext(Constraints, board, x, y))
                {
                    ++result.TryCount;
                    board.SetNumber(x, y, value);
                    if (board.IsConsistent(x, y, Constraints))
                    {
                        ++result.ConsistentTryCount;
                        if (RecursiveResolve(board, result))
                        {
                            return true;
                        }
                    }
                }
                board.ClearNumber(x, y);
            }
            return false;
        }
    }
}