initial commit

puzzle/nqueens/NBoard.cs

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+using System.Collections.Generic;
+using System.Linq;
+
+namespace nqueens
+{
+	public class NBoard
+	{
+		public readonly int[] Columns;
+
+		public int Size { get { return Columns.Length; } }
+		
+		public readonly int[] Conflicts;
+
+		public NBoard(int[] columns)
+		{
+			Columns = columns;
+			Conflicts = 
+				(from n in Enumerable.Range(0, Size)
+				select GetConflictCount(n)).ToArray();
+		}
+
+		public int GetQueenRow(int column)
+		{
+			return Columns[column];
+		}
+
+		public bool IsFeasible()
+		{
+			return Conflicts.All(c => c == 0);
+		}
+
+		public int GetConflictCount(int column)
+		{
+			return GetConflicts(column).Count;
+		}
+
+		public int TestConflictCount(int column, int row)
+		{
+			var originalRow = Columns[column];
+			Columns[column] = row;
+
+			var conflicts = GetConflictCount(column);
+
+			Columns[column] = originalRow;
+
+			return conflicts;
+		}
+
+		private List<int> GetConflicts(int column)
+		{
+			var queenRow = GetQueenRow(column);
+			var conflicts = new List<int>();
+			for (var iColumn = 0; iColumn < Size; iColumn++)
+			{
+				if (iColumn == column)
+					continue;
+				var iRow = Columns[iColumn];
+				if (iRow == queenRow)
+				{
+					conflicts.Add(iColumn);
+					continue;
+				}
+
+				var columnDiff = column - iColumn;
+				if (queenRow - columnDiff == iRow || queenRow + columnDiff == iRow)
+					conflicts.Add(iColumn);
+			}
+			return conflicts;
+		}
+
+		public void UpdateRow(int column, int row)
+		{
+			var oldConflictColumns = GetConflicts(column);
+			foreach (var i in oldConflictColumns)
+				Conflicts[i]--;
+
+			var sum = Conflicts.Any(c => c < 0);
+
+			Columns[column] = row;
+			
+			var newConflictColumns = GetConflicts(column);
+			Conflicts[column] = newConflictColumns.Count;
+			foreach (var i in newConflictColumns)
+				Conflicts[i]++;
+		}
+	}
+}