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

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

namespace uqac_ia_sudoku_csp.Solver.NextValueChoosers
{
    public class DhNextCellChooser : INextCellChooser
    {
        public void SelectVariable(Board board, out int x, out int y, IList<IConstraint> constraints)
        {
            var dict = new Dictionary<KeyValuePair<int, int>, int>();
            for (var yy = 0; yy < board.Size; ++yy)
            {
                for (var xx = 0; xx < board.Size; ++xx)
                {
                    if (board.GetNumber(xx, yy) == null)
                    {
                        var k = new KeyValuePair<int, int>(xx, yy);
                        if (!dict.ContainsKey(k))
                        {
                            dict.Add(k, 0);
                        }
                        ++dict[k];
                    }
                }
            }
            if (!dict.Any())
            {
                x = -1;
                y = -1;
            }
            else
            {
                var k = dict.OrderByDescending(pair => pair.Value).First().Key;
                x = k.Key;
                y = k.Value;
            }
        }
    }
}