找水王

遍历统计就很有可能创建出一个差不多和数据库一样大的内存空间，这样就是十分糟糕的情况。

package dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;

import com.sun.org.apache.regexp.internal.recompile;

public class Dao
{
    String findRyan()
    {

        String db_url = "jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8";
        String db_user = "root";
        String db_password = "";
        Connection conn = null;
        Statement state = null;
        ResultSet rs = null;
        ArrayList<String> list = new ArrayList<>();
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(db_url, db_user, db_password);
            state = conn.createStatement();
            rs = state.executeQuery("select uid,reid from post");
            while (rs.next())
            {
                String idList = rs.getString("uid") + "|" + rs.getString("reid");
                if (!(idList).equals(""))
                {
                    for (String id : idList.split("\|"))
                    {
                        list.add(id);
                    }
                }
            }
            ;
        } catch (Exception e)
        {
            e.printStackTrace();
        }
        System.out.println(list);
        for (int i = 0; i < list.size() - 1; i++)
        {
            if (!list.get(i).equals(list.get(i + 1)))
            {
                list.set(i, "a");
                list.set(i + 1, "a");
                i=i+1;
            }
        }
        System.out.println(list);
        return null;
    }

    public static void main(String[] args)
    {
        Dao aDao = new Dao();
        aDao.findRyan();
    }
}

于是有了一个取巧的方式，就是两两消去，利用“水王”有着过半数量的特性