C#大数阶乘算法

最新推荐文章于 2023-09-03 13:18:31 发布

赖张殷

最新推荐文章于 2023-09-03 13:18:31 发布

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本文介绍了一种使用C#实现的大数阶乘计算方法。通过将大整数分解为数组并利用循环进行逐位相乘的方式，实现了对极大数值阶乘的精确计算，并提供了完整的源代码。

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace 大数阶乘
{
    class Program
    {
        static void Main(string[] args)
        {
            Factorial fac = new Factorial(200000);
            fac.Calculate();
            Console.Write(fac.ToString());
            Console.ReadKey();
        }
    }

    public class Factorial
    {
        private int baseNumber = 100000;

        public int BaseNumber
        {
            get
            {
                return baseNumber;
            }
        }

        private int number;

        private List<int> result = new List<int>();

        public Factorial(int n)
        {
            number = n;
            result = new List<int>();
        }

        public List<int> Calculate()
        {
            int digit = (int)System.Math.Log10(baseNumber);
            int len = (int)(number * System.Math.Log10((number + 1) / 2) / digit);
            len += 2;

            int[] a = new int[len];
            int i, j;
            long c;
            int m = 0;

            a[0] = 1;
            for (i = 2; i <= number; i++)
            {
                c = 0;
                for (j = 0; j <= m; j++)
                {
                    long t = a[j] * i + c;
                    c = t / baseNumber;
                    a[j] = (int)(t % baseNumber);
                }
                while (c>0)
                {
                    m++;
                    a[m] = (int)(c % baseNumber);
                    c = c / baseNumber;
                }
            }
            for (i = 0; i <= m; i++)
            {
                result.Add(a[i]);
            }
            return result;
        }

        public override string ToString()
        {
            if(result .Count ==0)
            {
                Calculate();
            }

            StringBuilder sb = new StringBuilder();

            int digit = (int)System.Math.Log10(baseNumber);
            sb.Append(result[result.Count - 1]);

            for (int i = 0; i < result.Count; i++)
            {
                sb.Append(result[i].ToString().PadLeft(digit, '0'));
            }
            return sb.ToString();
        }
    }
}

转自：<a target=_blank href="http://http://www.cnblogs.com/snowdust/archive/2010/03/18/1688963.html">点击打开链接</a>