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using System; using System.Collections.Generic; using System.Linq; using Oyster.Math; namespace csdnTest { class Program { static void Main(string[] args) { DateTime beginTime = DateTime.Now; IntX result = Factorial(1000000); DateTime endTime = DateTime.Now; Console.WriteLine(endTime - beginTime); Console.WriteLine(result); Console.ReadKey(); } static IntX Factorial(int n) { int[] counter = GetPowCounter(n); SortedDictionaryIntX, bool sDict = new SortedDictionaryIntX, bool(); //计算幂乘并将结果压入优先队列(使用优化过的大数乘法,在计算相等规模的大数乘法时，效率最高) for (int i = 2; i = n; i++) { if (counter[i] 0) sDict.Add(IntX.Pow(i, (uint)counter[i]), false); } IntX valueA = 1, valueB; //用SortedDictionary模拟优先队列进行最后的计算 while (sDict.Count 1) { valueA = sDict.ElementAt(0).Key; valueB = sDict.ElementAt(1).Key; sDict.Remove(valueA); sDict.Remove(valueB); sDict.Add(valueA * valueB, false); } return sDict.ElementAt(0).Key; } //做质因数分解,以便使用幂乘进行计算 static int[] GetPowCounter(int n) { int[] pList = GetPrime(n); int[] pCounter = new int[n + 1]; for (int i = 0; i pList.Length; i++) { int k = n; while ((k /= pList[i]) 0) pCounter[pList[i]] += k; } return pCounter; } //生成质数列表 static int[] GetPrime(int n) { Listint prime = new Listint(); bool[] flags = new bool[n + 1]; for (int i = 2; i = n; i++) { if (!flags[i]) prime.Add(i); for (int j = 0; j prime.