uqac-ia-sudoku-csp/uqac-ia-sudoku-csp/Solver/NextValueChoosers/MRVNextValueChooser.cs

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

namespace uqac_ia_sudoku_csp.Solver.NextValueChoosers
{
    public class MRVNextValueChooser : INextValueChooser
    {
        public void SelectVariable(Board board, out int x, out int y, IList<IConstraint> constraints)
        {
            var avail = 1;
            while (avail < board.Size)
            {
                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)
                            {
                                x = xx;
                                y = yy;
                                return;
                            }
                        }
                    }
                }
                ++avail;
            }
            x = -1;
            y = -1;
        }

        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;
        }
    }
}