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优化M个数中取N个数的算法

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悬赏园豆:100 [待解决问题]

我想得到从36个数中取18个数的全部组合,这个组合有上亿种。

我采用递归计算,但是效率太低,运行时CPU和内存利用率不高,耗时太长,恳请高人赐教。

是否有多线程或其他更高效的算法取数。

  /// <param name="currentIndex">当前数组索引</param>
        /// <param name="remain">需取的个数</param>
        /// <param name="currentSelect">生成当前组合的字符串集合</param>
        /// <param name="Items">M个数集合</param>
        static void comb(int currentIndex, int remain, string currentSelect, string[] Items)
        {
            if (remain == 0)
            {
                //当此行不需取数时,列出此行取的N个数
                strResult += currentSelect + ";";
                return;
            }

            if (Items.Length - currentIndex < remain)
                return;
            //递归取数
            comb(currentIndex + 1, remain - 1, currentSelect + "," + Items[currentIndex], Items);
            comb(currentIndex + 1, remain, currentSelect, Items);
        }

鬼幻天使的主页 鬼幻天使 | 初学一级 | 园豆:77
提问于:2013-02-18 15:39
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所有回答(3)
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static void Main(string[] args)
        {
             for (int i = 0; i < Items.Length; i++)
            {
                System.Threading.Thread t = new System.Threading.Thread(new System.Threading.ParameterizedThreadStart(DoWork));
                t.Start(i);
            }

            //System.Threading.Thread.Sleep(10000);

            Console.Write(strResult.Length);
            Console.ReadLine();
        }
        static string[] Items = new string[] { "1", "2", "3", "4", "5", "6", "7", "8", "9", "10","11","12","13","14","15","16","17","18",
            "19","20","21","22","23","24","25","26","27","28","29","30","31","32","33","34","35","36"};
        static void DoWork(object o)
        {
            comb(int.Parse(o.ToString()), 18, "", Items);
        }
        
        static string strResult = "";
        /// <param name="currentIndex">当前数组索引</param>
        /// <param name="remain">需取的个数</param>
        /// <param name="currentSelect">生成当前组合的字符串集合</param>
        /// <param name="Items">M个数集合</param>
        static void comb(int currentIndex, int remain, string currentSelect, string[] Items)
        {
            if (Items.Length - currentIndex < remain)
                return;

            if (remain == 0)
            {
                //当此行不需取数时,列出此行取的N个数
                strResult += currentSelect + ";";
                return;
            }

            //递归取数
            comb(currentIndex + 1, remain - 1, currentSelect + "," + Items[currentIndex], Items);
        }


我换了一下多线程,不过还是很慢,

算法我感觉没有什么可优化的了,只能使用枚举的方式,便利所有可能,

从36个数中取18个数的全部组合,这个组合不止上亿种,

36的18次方等于 1.031442479849054e+28

一个28位的数字,即使每秒千亿次的计算,也会需要很长时间,不知道你这个算法需要用到什么应用上呢.?

希望能帮到你!!

只会造轮子 | 园豆:2448 (老鸟四级) | 2013-02-19 15:20

你好,算法确实没有什么可优化了,不过多线程可以稍微提高CPU的利用率(我还想.NET有没有其他机制可以提高运算效率)

这个算法是我业余爱好,研究彩票概率很感谢你的回复。

支持(0) 反对(0) 鬼幻天使 | 园豆:77 (初学一级) | 2013-02-19 21:12
0

这是个无解的问题,hash是否有用?

Alvin | 园豆:828 (小虾三级) | 2013-02-21 11:48
0

http://bbs.csdn.net/topics/300190422

Rookier | 园豆:652 (小虾三级) | 2013-02-21 17:59
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