用可变个数的ArrayList求素数
ArrayList可以充当一个可变的容器,有时候方便处理未知大小的一组数据。
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using System;
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using System.Collections; //为了使用ArrayList
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class prime
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{
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public static ArrayList arr=new ArrayList();
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public static void AddPrime(int arg){
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arr.Add(2);
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for (int i=3;i <= arg ;i++)
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{
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if(IsPrime(i)){
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arr.Add(i);
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}
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}
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}
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public static bool IsPrime(int arg){
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int i=0;
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while(Convert.ToInt16(arr[i]) * Convert.ToInt16(arr[i]) <=arg){
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if(arg % Convert.ToInt32(arr[i])==0) return false;
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i++;
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}
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//下面的方法完全正确,不过我决定尝试下ArrayList方法。
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/*
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foreach (int i in arr)
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{
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if(i*i <= arg){
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if(arg % i==0) return false;
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}else{
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break;
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}
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}
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*/
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return true;
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}
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public static void Main(){
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AddPrime(50);
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Console.WriteLine("50以内的素数有:");
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foreach(int i in arr){
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Console.Write("{0} ",i);
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}
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Console.WriteLine();
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Console.WriteLine("------------------------------------");
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Console.WriteLine("以下是ArrayList 对象的演示。");
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Console.Write("arr[1]:{0} ------- ",arr[1]); //这个打印不规范,arr[1] 为Object,但是仍然能够输出值。
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Console.Write("Convert.ToInt32(arr[1])*Convert.ToInt32(arr[1]):{0} ",Convert.ToInt32(arr[1])*Convert.ToInt32(arr[1])); //这个打印才是正确做法。
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}
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}
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代码下载:/Files/x116/prime.rar
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