100万个URL如何找到出现频率最高的前100个？

这个题是阿里的一个电话面试题，我想的头一个解决方案，有点限制，后面再写优化的

实验数据，python从百度抓得：

# -*- coding: utf-8 -*-
"""
Spyder Editor

This is a temporary script file.
"""

import urllib2
import re
import os

#connect to a URL
#一页的搜索结果中url大概是200个左右
file_url = open('url.txt','ab+')
#搜索框里的东西,这块可以设置成数字好让每次搜索的结果不一样
search = '123'
url = "http://www.baidu.com/s?wd="+search

def setUrlToFile():
    website = urllib2.urlopen(url)
    #read html code 

    html = website.read() 

    #use re.findall to get all the links 

    links = re.findall('"((http|ftp)s?://.*?)"', html)

    for s in links:
        print s[0]
        if len(s[0]) < 256:
            file_url.write(s[0]+'\r\n')

#收集实验数据
for i in range(0,50):
    setUrlToFile()

file_url.close()

###需要重新打开再读一下
file_url = open('url.txt','r')
file_lines = len(file_url.readlines())
print "there are %d url in %s" %(file_lines,file_url)
file_url.close()

c++  写的读 url.xml,放到map里面，对map<string , int>的value进行排序，得到前100个，运行一下也就55s，还是很快的，url长度进行了限制小于256个字符：

#pragma once
/*
//计算代码段运行时间的类
//
*/
#include <iostream>

#ifndef ComputeTime_h
#define ComputeTime_h

//单位毫秒

class   ComputeTime
{
private:
	int Initialized;
	__int64 Frequency;
	__int64 BeginTime;  

public:  

	bool Avaliable();
	double End();
	bool Begin();
	ComputeTime();
	virtual   ~ComputeTime();    

};  

#endif
#include "stdafx.h"
#include "ComputeTime.h"
#include <iostream>
#include <Windows.h>

ComputeTime::ComputeTime()
{
	Initialized=QueryPerformanceFrequency((LARGE_INTEGER   *)&Frequency);
}  

 ComputeTime::~ComputeTime()
{  

}  

 bool   ComputeTime::Begin()
{
	if(!Initialized)
		return 0;

	 return   QueryPerformanceCounter((LARGE_INTEGER   *)&BeginTime);
 }

 double   ComputeTime::End()
{
	 if(!Initialized)
		return 0;

	 __int64   endtime;  

	 QueryPerformanceCounter((LARGE_INTEGER   *)&endtime);  

	 __int64   elapsed = endtime-BeginTime;  

	 return   ((double)elapsed/(double)Frequency)*1000.0;  //单位毫秒
 }  

 bool   ComputeTime::Avaliable()
{
	 return Initialized;
}   

// sortUrl.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
//#include <utility>
#include <vector>
#include <map>
#include <fstream>
#include <iostream>
#include <string>
#include <algorithm>
#include "ComputeTime.h"

using namespace std;

map<string,int> urlfrequency;

typedef pair<string, int> PAIR;

struct CmpByValue
{
	bool operator()(const PAIR& lhs, const PAIR& rhs)
	{
		return lhs.second > rhs.second;
	}
};

void find_largeTH(map<string,int> urlfrequency)
{
	//把map中元素转存到vector中 ,按照value排序
	vector<PAIR> url_quency_vec(urlfrequency.begin(), urlfrequency.end());
	sort(url_quency_vec.begin(), url_quency_vec.end(), CmpByValue());
	//url_quency_vec.size()
	for (int i = 0; i != 100; ++i)
	{
		cout<<url_quency_vec[i].first<<endl;
		cout<<url_quency_vec[i].second<<endl;
	}
}

//urlheap的建立过程，URL插入时候存在的
void insertUrl(string url)
{
	pair<map<string ,int>::iterator, bool> Insert_Pair;
	Insert_Pair = urlfrequency.insert(map<string, int>::value_type(url,1));

	if (Insert_Pair.second == false)
	{
		(Insert_Pair.first->second++);
	}

}

int _tmain(int argc, _TCHAR* argv[])
{
	fstream URLfile;
	char buffer[1024];
	URLfile.open("url.txt",ios::in|ios::out|ios::binary);

	if (! URLfile.is_open())
	{ cout << "Error opening file"; exit (1); }
	else
	{
	cout<<"open file success!"<<endl;
	}

	ComputeTime cp;
	cp.Begin();
	int i = 0;
	 while (!URLfile.eof())
	{
	URLfile.getline (buffer,1024);
	//cout << buffer << endl;
	string temp(buffer);
	//cout<<i++<<endl;
	insertUrl(temp);
	}  

	find_largeTH(urlfrequency);

	cout<<"running time: "<<cp.End()<<"ms"<<endl;

	getchar();
	//system("pause");
	return 0;
}

实验结果：



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