设A={1,2,3,4,5,6},Ra={<x,y>|x,y∈A,y≡(mod3)}，画出关系图，写出Ra的所有等价类

以下是Ra的关系图：

1 -> 4
1 -> 1
2 -> 5
2 -> 2
3 -> 6
3 -> 3
4 -> 1
4 -> 4
5 -> 2
5 -> 5
6 -> 3
6 -> 6

等价类是将A中的元素分组，使得同一组中的元素关于Ra等价。根据Ra的定义，我们可以将A分成三个等价类：

{1, 4}
{2, 5}
{3, 6}

相关问题

在Java中用Dom4j把这一段xml内容转成Map对象：<?xml version="1.0" encoding="UTF-8"?> <java version="1.6.0_26" class="java.beans.XMLDecoder"> <object class="java.util.HashMap"> <void method="put"> <string>att_20160719180419281NEk9</string> <string>cx</string> </void> <void method="put"> <string>att_20160511094248589ZKYq</string> <string>cnmm</string> </void> <void method="put"> <string>att_20161018153614188aTus</string> <string>zsx;fj</string> </void> <void method="put"> <string>att_20160422110906494XuEf</string> <null/> </void> <void method="put"> <string>att_20160511130210612UULE</string> <string>fjyxapp;jjgjapp;wx;jd;dxjg;tb;wsjy</string> </void> <void method="put"> <string>att_20160719180542840LnFm</string> <string></string> </void> <void method="put"> <string>att_20160511130025203ssle</string> <string>zdgsszta</string> </void> <void method="put"> <string>att_20160810131359346N0ra</string> <string>szjys</string> </void> <void method="put"> <string>att_20160511130031927equg</string> <string></string> </void> <void method="put"> <string>att_20160422110456036qp7Y</string> <null/> </void> <void method="put"> <string>att_20160422110543585f7iI</string> <string>cpjbxx</string> </void> </object> </java>

您可以使用以下代码将该XML转换为Map对象：

import java.io.StringReader;
import java.util.HashMap;
import java.util.Map;

import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class XmlToMap {
    public static void main(String[] args) throws Exception {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>  <java version=\"1.6.0_26\" class=\"java.beans.XMLDecoder\">   <object class=\"java.util.HashMap\">    <void method=\"put\">     <string>att_20160719180419281NEk9</string>     <string>cx</string>    </void>    <void method=\"put\">     <string>att_20160511094248589ZKYq</string>     <string>cnmm</string>    </void>    <void method=\"put\">     <string>att_20161018153614188aTus</string>     <string>zsx;fj</string>    </void>    <void method=\"put\">     <string>att_20160422110906494XuEf</string>     <null/>    </void>    <void method=\"put\">     <string>att_20160511130210612UULE</string>     <string>fjyxapp;jjgjapp;wx;jd;dxjg;tb;wsjy</string>    </void>    <void method=\"put\">     <string>att_20160719180542840LnFm</string>     <string></string>    </void>    <void method=\"put\">     <string>att_20160511130025203ssle</string>     <string>zdgsszta</string>    </void>    <void method=\"put\">     <string>att_20160810131359346N0ra</string>     <string>szjys</string>    </void>    <void method=\"put\">     <string>att_20160511130031927equg</string>     <string></string>    </void>    <void method=\"put\">     <string>att_20160422110456036qp7Y</string>     <null/>    </void>    <void method=\"put\">     <string>att_20160422110543585f7iI</string>     <string>cpjbxx</string>    </void>   </object>  </java>";
        Map<String, String> map = xmlToMap(xml);
        System.out.println(map);
    }

    public static Map<String, String> xmlToMap(String xml) throws Exception {
        Map<String, String> map = new HashMap<>();
        SAXReader reader = new SAXReader();
        Document document = reader.read(new StringReader(xml));
        Element root = document.getRootElement().element("object");
        for (Element element : root.elements("void")) {
            Element keyElement = element.element("string");
            Element valueElement = element.elements().get(1);
            String key = keyElement.getText();
            String value = valueElement == null ? null : valueElement.getText();
            map.put(key, value);
        }
        return map;
    }
}

该代码使用Dom4j库解析XML，并将其转换为Map对象。输出结果为:

{att_20160719180419281NEk9=cx, att_20160511094248589ZKYq=cnmm, att_20161018153614188aTus=zsx;fj, att_20160422110906494XuEf=null, att_20160511130210612UULE=fjyxapp;jjgjapp;wx;jd;dxjg;tb;wsjy, att_20160719180542840LnFm=, att_20160511130025203ssle=zdgsszta, att_20160810131359346N0ra=szjys, att_20160511130031927equg=, att_20160422110456036qp7Y=null, att_20160422110543585f7iI=cpjbxx}

解释一下int a=1，b=2，&ra=a，&rb=b

这段代码定义了两个整型变量a和b，并且将它们分别赋值为1和2。&ra=a和&rb=b分别定义了两个指针变量ra和rb，并且将它们分别指向a和b所在的内存地址。因此，通过ra和rb指针变量，可以修改a和b的值。可以使用以下示例代码来理解：

#include <iostream>
using namespace std;

int main() {
    int a = 1, b = 2;
    int& ra = a;    // 定义ra指向a
    int& rb = b;    // 定义rb指向b

    cout << "a = " << a << ", b = " << b << endl;    // 输出a和b的值
    cout << "ra = " << ra << ", rb = " << rb << endl; // 输出ra指向的值和rb指向的值

    ra = 3;    // 修改ra指向的值，也就是a的值
    rb = 4;    // 修改rb指向的值，也就是b的值

    cout << "a = " << a << ", b = " << b << endl;    // 输出修改后的a和b的值
    cout << "ra = " << ra << ", rb = " << rb << endl; // 输出修改后ra指向的值和rb指向的值

    return 0;
}

输出结果为：

a = 1, b = 2
ra = 1, rb = 2
a = 3, b = 4
ra = 3, rb = 4

可以看到，通过ra和rb指针变量修改a和b的值，也就是间接修改了a和b所在的内存地址中的值。