A class which maps a fixed size array of integer bijective to a single integer.

BijectivMap.cs

namespace Hediet.Math
{
    public class BijectivMap
    {
        private readonly int[] lowerKeyBounds;
        private readonly int[] upperKeyBounds;

        public BijectivMap(int[] lowerKeyBounds, int[] upperKeyBounds)
        {
            this.lowerKeyBounds = lowerKeyBounds;
            this.upperKeyBounds = upperKeyBounds;
            if (upperKeyBounds.Length != lowerKeyBounds.Length)
                throw new ArgumentException("upperKeyBounds.length is invalid");
        }

        public int Minimum { get { return 0; } }
        public int Maximum
        {
            get
            {
                return lowerKeyBounds.Select((c, i) => upperKeyBounds[i] - c + 1).Aggregate(1, (a, b) => a * b) - 1;
            }
        }

        public int[] GetKeys(int value)
        {
            int[] result = new int[lowerKeyBounds.Length];
            for (int i = result.Length - 1; i >= 0; i--)
            {
                int factor = (upperKeyBounds[i] - lowerKeyBounds[i] + 1);
                result[i] = (value % factor) + lowerKeyBounds[i];
                value /= factor;
            }
            return result;
        }

        public int GetValue(params int[] keys)
        {
            if (keys.Length != lowerKeyBounds.Length)
                throw new ArgumentException("keys.length is invalid");
            int result = 0;
            for (int i = 0; i < keys.Length; i++)
            {
                result = result * (upperKeyBounds[i] - lowerKeyBounds[i] + 1)
                         + (keys[i] - lowerKeyBounds[i]);
            }
            return result;
        }
    }
}