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C#工具类之素数扩展类
/// <summary> /// 素数帮忙类 /// 本类是从.net源码 类 internal static class HashHelpers 类里抽取相应的代码 /// https://referencesource.microsoft.com/#mscorlib/system/collections/hashtable.cs,e8668bf19da49963 /// Hashtable.cs里 /// </summary> public class PrimeHelper { /// <summary> /// 给定一些素数(除了2) /// </summary> public static readonly int[] Primes = { 3, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293, 353, 431, 521, 631, 761, 919, 1103, 1327, 1597, 1931, 2333, 2801, 3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591, 17519, 21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523, 108631, 130363, 156437, 187751, 225307, 270371, 324449, 389357, 467237, 560689, 672827, 807403, 968897, 1162687, 1395263, 1674319, 2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369}; /// <summary> /// 判断是否是素数 /// </summary> /// <param name="candidate"></param> /// <returns></returns> public static bool IsPrime(int candidate) { //偶数当然不是素数 if ((candidate & 1) != 0) { int limit = (int)Math.Sqrt(candidate); for (int divisor = 3; divisor <= limit; divisor += 2) { if ((candidate % divisor) == 0) return false; } return true; } //2是素数 return (candidate == 2); } /// <summary> /// 大于给定数的最小素数 /// </summary> /// <param name="min"></param> /// <returns></returns> public static int GetPrime(int min) { if (min < 0) { throw new ArgumentException("给定数必须是自然数"); } //先从给定数组里找 foreach (int prime in Primes) { if (prime >= min) { return prime; } } //给定数组里没有相应的素数,则循环找 //如果min是偶数,则起始值为加1,否则起始值为本身 for (int i = (min | 1); i < Int32.MaxValue; i += 2) { if (IsPrime(i) ) return i; } return min; } /// <summary> /// 获取最小素数(2除外) /// </summary> /// <returns></returns> public static int GetMinPrime() { return Primes[0]; } }
C#工具类之素数扩展类
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