给定a、b两个文件，各存放50亿个url，每个url各占64字节，内存限制是4G，让你找出a、b文件共同的url?

package com.hadoop.hdfs;

import org.apache.hadoop.yarn.webapp.hamlet.Hamlet;

import org.junit.Test;

import java.io.*;

import java.util.HashMap;

import java.util.HashSet;

public class Suanfa1 {

    @Test

    public void a1() throws IOException {

        BufferedReader bufferedReader = new BufferedReader(new FileReader("D:/aa.txt"));

//        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://"))

        String str1 = "";

        while ((str1 = bufferedReader.readLine())!=null){

            int i = (int) (hashCode(str1)%1000);

            BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://aa"+String.valueOf(i)+".txt"));

            bufferedWriter.write(str1);

            bufferedWriter.close();

            System.out.println(i);

        }

        bufferedReader.close();

    }

    public void a2() throws IOException {

        BufferedReader bufferedReader = new BufferedReader(new FileReader("D:/bb.txt"));

//        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://"))

        String str1 = "";

        while ((str1 = bufferedReader.readLine())!=null){

            int i = (int) (hashCode(str1)%1000);

            BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://bb"+String.valueOf(i)+".txt"));

            bufferedWriter.write(str1);

            bufferedWriter.close();

        }

        bufferedReader.close();

    }

    public long hashCode(String str) {

        long h = 0;

        if (h == 0) {

            int off = 0;

            char val[] = str.toCharArray();

            long len = str.length();

            for (long i = 0; i < len; i++) {

                h = 31 * h + val[off++];

            }

        }

        return h;

    }

    @Test

    public void a3() throws IOException {

        a1();

        a2();

        for (int i = 0; i < 1000; i++) {

            BufferedReader bufferedReader1 = new BufferedReader(new FileReader("D://aa"+String.valueOf(i)+".txt"));

            BufferedReader bufferedReader2 = new BufferedReader(new FileReader("D://bb"+String.valueOf(i)+".txt"));

            HashSet set = new HashSet();

            String input1 = "";

            while ((input1 = bufferedReader1.readLine())!=null){

                set.add(hashCode(bufferedReader1.readLine()));

            }

            String input2 = "";

            while ((input2 = bufferedReader2.readLine())!=null){

                if (set.contains(hashCode(input2))){

                    System.out.println(input2);

                }

            }

        }

    }

}