RadixSorter.cs

namespace Algorithms.Sorters.Integer
{
    /// <summary>
    ///     Radix sort is a non-comparative integer sorting algorithm that sorts data with integer keys by grouping keys by the
    ///     individual
    ///     digits which share the same significant position and value. A positional notation is required, but because integers
    ///     can represent
    ///     strings of characters (e.g., names or dates) and specially formatted floating point numbers, radix sort is not
    ///     limited to integers.
    /// </summary>
    public class RadixSorter : IIntegerSorter
    {
        /// <summary>
        ///     Sorts array in ascending order.
        /// </summary>
        /// <param name="array">Array to sort.</param>
        public void Sort(int[] array)
        {
            var bits = 4;
            var b = new int[array.Length];
            var rshift = 0;
            for (var mask = ~(-1 << bits); mask != 0; mask <<= bits, rshift += bits)
            {
                var cntarray = new int[1 << bits];
                foreach (var t in array)
                {
                    var key = (t & mask) >> rshift;
                    ++cntarray[key];
                }

                for (var i = 1; i < cntarray.Length; ++i)
                {
                    cntarray[i] += cntarray[i - 1];
                }

                for (var p = array.Length - 1; p >= 0; --p)
                {
                    var key = (array[p] & mask) >> rshift;
                    --cntarray[key];
                    b[cntarray[key]] = array[p];
                }

                var temp = b;
                b = array;
                array = temp;
            }
        }
    }
}