.Net集合算法举例

using System;
namespace Rabbit.Tools
{
    public static class SetAlgorithms
    {
        /// <summary>
        /// 集合算法的回调
        /// </summary>
        /// <param name="result">运算结果</param>
        /// <param name="length">运算结果有效长度</param>
        /// <returns>控制算法是否继续,如果要结束算法,返回false</returns>
        /// <remarks>回调中不要修改result中的值,否则可能引起不可预知的后果</remarks>
        public delegate bool SetAlgorithmCallback (int[] result,int length);
        //argument check for arrangement and combination
        static bool CheckNM(int n, int m)
        {
            if (m > n || m < 0 || n < 0)
                throw new ArgumentException();
            if (m == 0 || n == 0)
                return false;
            return true;
        }
        static bool Arrangement(int n, int rlen, int[] result, SetAlgorithmCallback callback)
        {
            if (rlen == result.Length)
                return callback(result, rlen);
            for (var i = 0; i < n; ++i)
            {
                //skip used element
                bool skip = false;
                
                for (var j = 0; j < rlen; ++j)
                {
                    if (result[j] == i)
                    {
                        skip = true;
                        break;
                    }
                }
                if (skip)
                    continue;
                //set element index
                result[rlen] = i;
                //recurrent next
                if (!Arrangement(n, rlen + 1, result, callback))
                    return false;
            }
            return true;
        }
        /// <summary>
        /// 求排列A(n,m)
        /// </summary>
        /// <param name="n">集合元素个数</param>
        /// <param name="m">取出元素个数</param>
        /// <param name="callback">回调</param>
        public static void Arrangement(int n, int m, SetAlgorithmCallback callback)
        {
            if (!CheckNM(n, m))
                return;
            var result = new int[m];
            for (var i = 0; i < n; ++i)
            {
                result[0] = i;
                if (!Arrangement(n, 1, result, callback))
                    return;
            }
        }
        static bool Combination(int n,int m, int i, int rlen, int[] result, SetAlgorithmCallback callback)
        {
            if (rlen == m)
                return callback(result, rlen);
            for (var j = ++i; j < n; ++j)
            {
                result[rlen] = j;
                if (!Combination(n,m, j, rlen + 1, result, callback))
                    return false;
            }
            return true;
        }
        /// <summary>
        /// 求组合C(n,m)
        /// </summary>
        /// <param name="n">集合元素个数</param>
        /// <param name="m">取出元素个数</param>
        /// <param name="callback">回调</param>
        public static void Combination(int n, int m, SetAlgorithmCallback callback)
        {
            if (!CheckNM(n, m))
                return;
            int[] result;
            result = new int[n];
            for (var i = 0; i < n; ++i)
            {
                result[0] = i;
                if (!Combination(n,m, i, 1, result,callback))
                    return;
            }
        }
        static bool SubSet(int n, int i, int rlen, int[] result, SetAlgorithmCallback callback)
        {
            if (!callback(result, rlen))
                return false;
            if (rlen == n - 1)
                return true;
            for (var j = ++i; j < n; ++j)
            {
                result[rlen] = j;
                if (!SubSet(n, j, rlen + 1, result, callback))
                    return false;
            }
            return true;
        }
        /// <summary>
        /// 求除空集外包含n个元素的集合的真子集
        /// </summary>
        /// <param name="n">集合元素个数</param>
        public static void SubSet(int n, SetAlgorithmCallback callback)
        {
            if (n < 0)
                throw new ArgumentException();
            if (n == 0)
                return;
            var result = new int[n - 1];
            for (var i = 0; i < n; ++i)
            {
                result[0] = i;
                if (!SubSet(n, i, 1, result, callback))
                    return;
            }
        }
        static bool CartesianProduct(int[] sets, int i, int[] result, SetAlgorithmCallback callback)
        {
            for (var j = 0; j < sets[i]; ++j)
            {
                result[i] = j;
                if (i == sets.Length - 1)
                {
                    if (!callback(result, i))
                        return false;
                }
                else
                {
                    if (!CartesianProduct(sets, i + 1, result, callback))
                        return false;
                }
            }
            return true;
        }
        /// <summary>
        /// 求集合笛卡尔积
        /// </summary>
        /// <param name="sets">包含集合元素个数的数组</param>
        /// <param name="callback">回调函数</param>
        public static void CartesianProduct(int[] sets, SetAlgorithmCallback callback)
        {
            int[] result = new int[sets.Length];
            CartesianProduct(sets, 0, result, callback);
        }
    }
}