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锁定老帖子 主题：判断质数以及求某数以内的质数
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发表时间：2007-11-26
xml 代码
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发表时间：2008-01-21
请使用线性筛法
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发表时间：2008-01-22
package com.maodajun.javaeye5;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class SingleWord {
List list = new ArrayList();
/**
* 将list中的数据求合
* @return
*/
public int addAll(){
int all = 0 ;
String temp = null;
for(Iterator it = list.iterator();it.hasNext();){
temp = (String) it.next();
all += Integer.parseInt(temp);
}
return all;
}
/**
* @deprecated
* 已过时方法
* 用于判断是否是质数
* @param str
*/
public void isSingle(String str){
int tmp = Integer.parseInt(str);
if(tmp<2){
return;
}
for(int i = 2 ; Math.sqrt(tmp) >=i ; i ++ ){
if(tmp%i==0){
return;
}
}
list.add(str);
}
/**
* 用来找到所有小于str的质数方法
*
*/
public void findAllSingle(String str){
int tmp = Integer.parseInt(str);
for(int i = 0 ; tmp >i ;i ++){
isOldSingle(""+i);
}
}
/**
* 对输入的数值与已有的数值对比
* 看可否被整除.
*
* @param str
*/
public void isOldSingle(String str){
int tmp = Integer.parseInt(str);
if(tmp<2){
return;
}else{
for(int i = 0 ; list.size()>i ;i++ ){
int single =Integer.parseInt(list.get(i).toString());
if(tmp%single ==0){
return;
}
}
}
list.add(str);
}
public List getList() {
return list;
}
public void setList(List list) {
this.list = list;
}
}
package com.maodajun.javaeye5;
import java.util.ArrayList;
import java.util.List;
import junit.framework.TestCase;
public class SingleWordTest extends TestCase {
public static void main(String[] args) {
junit.textui.TestRunner.run(SingleWordTest.class);
}
public SingleWordTest(String arg0) {
super(arg0);
}
protected void setUp() throws Exception {
super.setUp();
}
protected void tearDown() throws Exception {
super.tearDown();
}
/*
* Test method for 'com.maodajun.javaeye5.SingleWord.addAll()'
*/
public void testAddAll() {
List list = new ArrayList();
list.add("1");
list.add("2");
SingleWord singleword = new SingleWord();
singleword.setList(list);
int i = singleword.addAll();
assertEquals(3,i);
}
public void testIsSingle(){
SingleWord singleword = new SingleWord();
singleword.isSingle("0");
assertEquals(0,singleword.getList().size());
singleword.isSingle("1");
assertEquals(0,singleword.getList().size());
singleword.isSingle("4");
assertEquals(0,singleword.getList().size());
singleword.isSingle("2");
assertEquals(1,singleword.getList().size());
singleword.isSingle("3");
assertEquals(2,singleword.getList().size());
singleword.isSingle("13");
assertEquals(3,singleword.getList().size());
singleword.isSingle("25");
assertEquals(3,singleword.getList().size());
}
public void testIsOldSingle(){
SingleWord singleword = new SingleWord();
singleword.isOldSingle("0");
assertEquals(0,singleword.getList().size());
singleword.isOldSingle("1");
assertEquals(0,singleword.getList().size());
singleword.isOldSingle("2");
assertEquals(1,singleword.getList().size());
singleword.isOldSingle("3");
assertEquals(2,singleword.getList().size());
singleword.isOldSingle("4");
assertEquals(2,singleword.getList().size());
singleword.isOldSingle("5");
assertEquals(3,singleword.getList().size());
singleword.isOldSingle("6");
assertEquals(3,singleword.getList().size());
}
public void testFindAllSingle(){
SingleWord singleword = new SingleWord();
singleword.findAllSingle("10");
assertEquals(17,singleword.addAll());
singleword .setList(new ArrayList());
singleword.findAllSingle("20");
assertEquals(77,singleword.addAll());
}
}
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发表时间：2008-01-26
来个Erlang版本的： -module(test).
-export([main/1]).
main(N) ->
L = calc(N, []),
S = lists:foldl(fun(X, Total) -> Total+X end, 0, L),
io:format("质数：~p~n", [L]),
io:format("总和：~p~n", [S]).
%统计某个数以内的所有质数
calc(1, L) -> L;
calc(N, L) ->
case is_single(N) of
false -> calc(N-1, L);
true -> calc(N-1, [N|L])
end.
%判断是否是质数
is_single(N) -> is_single(N, N-1).
is_single(_N, 1) -> true;
is_single(N, D) when N rem D ==0 -> false;
is_single(N, D) -> is_single(N, D-1).
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