uqac-ia-sudoku-csp/uqac-ia-sudoku-csp/Solver/NextCellChoosers/MrvNextCellChooser.cs

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

namespace uqac_ia_sudoku_csp.Solver.NextValueChoosers
{
    public class MrvNextCellChooser : INextCellChooser
    {
        private readonly INextCellChooser _nextCellChooser;

        public MrvNextCellChooser(INextCellChooser nextCellChooser)
        {
            _nextCellChooser = nextCellChooser;
        }

        public void SelectVariable(Board board, out int x, out int y, IList<IConstraint> constraints)
        {
            var avail = 1;
            var vars = new List<KeyValuePair<int, int>>();
            while (avail <= board.Size && vars.Count == 0)
            {
                for (var xx = 0; xx < board.Size; ++xx)
                {
                    for (var yy = 0; yy < board.Size; ++yy)
                    {
                        if (board.GetNumber(xx, yy) == null)
                        {
                            var remaining = GetRemainingValue(board, xx, yy, constraints);
                            if (remaining == avail)
                            {
                                vars.Add(new KeyValuePair<int, int>(xx, yy));
                            }
                        }
                    }
                }
                ++avail;
            }
            if (vars.Count == 0)
            {
                x = -1;
                y = -1;
            }
            else if (vars.Count == 1 || _nextCellChooser == null)
            {
                x = vars[0].Key;
                y = vars[0].Value;
            }
            else
            {
                _nextCellChooser.SelectVariable(board, out x, out y, constraints);
            }
        }

        protected int GetRemainingValue(Board board, int x, int y, IList<IConstraint> constraints)
        {
            var c = 0;
            for (var i = 0; i < board.Size; ++i)
            {
                board.SetNumber(x, y, i);
                if (board.IsConsistent(x, y, constraints))
                {
                    ++c;
                }
            }
            board.ClearNumber(x, y);
            return c;
        }
    }
}