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qiezi的學習園地

AS/C/C++/D/Java/JS/Python/Ruby
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周末抽空做了點小測試，根據http://blog.vckbase.com/jzhang/archive/2006/03/28/18807.html中m網友修改的算法，python版本中讀取所有行以后就做一個排序，再去除重復項。這個算法在我的機器上執行時間是1735ms左右，屬于python版本中最快的一個。

D版本暫還沒想到有更優化的做法，D在處理以char[]作key的關聯數組時，判斷方法是先判斷hash，如果hash相等，則繼續做字符串判斷。它執行時間是1120ms左右。

以D版本為基礎，自己寫了一個C＋＋的Email類：

class?Email
{
private:
????????string?mail;
????????size_t?hash;
????????friend?bool?operator?<?(const?Email&?lhs,?const?Email&?rhs);
public:
????????Email?(const?char*?mail_)
????????????????:?mail(mail_),?hash(my_hash(mail_))
????????{
????????}
};

bool?operator?<?(const?Email&?lhs,?const?Email&?rhs)
{
????????if?(lhs.hash?==?rhs.hash)
????????????????return?lhs.mail?<?rhs.mail;
????????return?lhs.hash?<?rhs.hash;
}

把它插入set并判斷是否有重復。

這個程序由于string的大量拷貝，以及大量內存分配，執行時間相當長，在我的機器上是5s左右。D和python版本由于對象拷貝成本較低，加上都有內存分配策略，自然有一些優勢。

退而求其次，既然hash沖突的幾率較低，試試只保存hash：

class?Email
{
private:
????????size_t?hash;
????????friend?bool?operator?<?(const?Email&?lhs,?const?Email&?rhs);
public:
????????Email?(const?char*?mail_)
????????????????:?hash(my_hash(mail_))
????????{
????????}
};

bool?operator?<?(const?Email&?lhs,?const?Email&?rhs)
{
????????return?lhs.hash?<?rhs.hash;
}

這次測試就比較快了，耗時僅1020ms左右，比D版本還要快，當然它不是完善的版本。

考慮到構造成本，于是改為只用一個set<int>來保存hash值再測試，這次耗時是930ms。

實際上可以做一個改進的C＋＋版本，一次性讀入文件的全部內容到一個大緩沖區，把所有的\n字符修改為\0，用一個動態數組保存緩沖區的所有字符串指針，hash值也須計算并保存到數組。再用D的索引方式，先hash比較，再字符串比較，效率應該也不低。

實現了一個：
#include?<iostream>
#include?<string>
#include?<set>
#include?<fstream>
#include?<iterator>
#include?<sys/time.h>
using?namespace?std;


size_t?my_hash?(const?char*?str)
{
????????size_t?ret?=?0;
????????while?(*str)
????????????????ret?=?11?*?ret?+?*str++;
????????return?ret;
}

class?Email
{
private:
????????size_t?hash;
????????const?char*?mail;
????????friend?bool?operator?<?(const?Email&?lhs,?const?Email&?rhs);
public:
????????Email?(const?char*?mail_)
????????????????:?hash(my_hash(mail_)),?mail(mail_)
????????{
????????}
};

bool?operator?<?(const?Email&?lhs,?const?Email&?rhs)
{
????????if?(lhs.hash?==?rhs.hash)
????????????????return?strcmp(lhs.mail,?rhs.mail)?<?0;
????????return?lhs.hash?<?rhs.hash;
}

int?main(int?argc,?char**?argv)
{
????????if?(argc?<?3)
????????{
????????????????cout?<<?"Wrong?arguments"?<<?endl;
????????????????return?1;
????????}

????????FILE*?fin?=?fopen(argv[1],?"r");
????????if?(!fin)
????????{
????????????????cout?<<?"Invalid?input?file"?<<?endl;
????????????????return?2;
????????}
????????FILE*?fout?=?fopen(argv[2],?"w");
????????if?(!fout)
????????{
????????????????fclose(fin);
????????????????cout?<<?"Invalid?output?file"?<<?endl;
????????????????return?3;
????????}

????????timeval?start,?end;

????????const?int?BUF_SIZE?=?20?*?1024?*?1024;
????????char*?buffer?=?new?char[BUF_SIZE];
????????memset(buffer,?0,?BUF_SIZE);

????????gettimeofday(&start,?0);
????????set<Email>?emails;

????????size_t?read?=?fread?(buffer,?BUF_SIZE,?1,?fin);
????????char*?begin?=?buffer;
????????char*?current?=?buffer;

????????while?(*current?!=?'\0')
????????{
????????????????if?(*current?==?'\n')
????????????????{
????????????????????????*current?=?'\0';
????????????????????????if?(emails.insert(begin).second){
????????????????????????????????fputs(begin,?fout);
????????????????????????????????fwrite("\n",?1,?1,?fout);
????????????????????????}
????????????????????????begin?=?current?+?1;
????????????????}
????????????????++?current;
????????}

??????? fclose(fout);
??????? fclose(fin);

????????gettimeofday(&end,?0);

????????printf("Time?used:?%d?ms\n",?((end.tv_sec?-?start.tv_sec)?*?1000?+?(end.tv_usec?-?start.tv_usec)?/?1000));

??????? delete[] buffer;
????????return?0;
}

memset不是必須的，不過我不知道如何獲取讀入的大小。fread讀取后，如果讀到EOF，則返回值為0。所以我這里用memset先初始化內存，但不把它計入耗時。new操作也沒計入，因為其它語言比如python、D在啟動時都由運行時做了類似工作。

這個程序在我的機器上耗時為1350ms左右。我想可慢在set上，對象拷貝？內存分配？

做了幾個優化版本，沒多大提高。

重新測試了下：
A、python(m網友版本）：
lijie t # python test.py
1689.0411377
lijie t # python test.py
1711.40599251
lijie t # python test.py
1699.63312149
lijie t # python test.py
1712.00013161
lijie t # python test.py
1713.8838768

B、D版本：
lijie t # ./testd email.txt email-new.txt
1091
lijie t # ./testd email.txt email-new.txt
1070
lijie t # ./testd email.txt email-new.txt
1062
lijie t # ./testd email.txt email-new.txt
1062
lijie t # ./testd email.txt email-new.txt
1096

C、C＋＋只比較hash，set<Email>版本：
lijie t # ./test3 email.txt email-new.txt
Time used: 981 ms
lijie t # ./test3 email.txt email-new.txt
Time used: 1000 ms
lijie t # ./test3 email.txt email-new.txt
Time used: 980 ms
lijie t # ./test3 email.txt email-new.txt
Time used: 986 ms
lijie t # ./test3 email.txt email-new.txt
Time used: 987 ms

D、C＋＋只比較hash，set<int>版本：
lijie t # ./test4 email.txt email-new.txt
Time used: 951 ms
lijie t # ./test4 email.txt email-new.txt
Time used: 953 ms
lijie t # ./test4 email.txt email-new.txt
Time used: 947 ms
lijie t # ./test4 email.txt email-new.txt
Time used: 950 ms
lijie t # ./test4 email.txt email-new.txt
Time used: 962 ms

E、C＋＋大緩沖區，比較hash和字符串，set<Email>版本：
lijie t # ./test5 email.txt email-new.txt
Time used: 1375 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1359 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1369 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1378 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1396 ms

F、C＋＋大緩沖區，比較字符串版本：
lijie t # ./test6 email.txt email-new.txt
Time used: 1168 ms
lijie t # ./test6 email.txt email-new.txt
Time used: 1169 ms
lijie t # ./test6 email.txt email-new.txt
Time used: 1171 ms
lijie t # ./test6 email.txt email-new.txt
Time used: 1179 ms
lijie t # ./test6 email.txt email-new.txt
Time used: 1169 ms

從C、E和F來看，對象拷貝成本是比較高的，E版本僅僅比C版本多了個const char*成員變量，hash值比較散，很少會真的執行到strcmp。保持E版本對象結構不變，把operator <里面的實現改為C版本，測試結果如下：
lijie t # ./test5 email.txt email-new.txt
Time used: 1355 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1360 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1348 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1353 ms
lijie t # ./test5 email.txt email-new.txt
Time used: 1379 ms

效率只提高了一點點，這個版本僅僅比C版本多了個成員變量拷貝，竟然慢了這么多。說明Email對象的2個成員變量拷貝成本的確很高。

F版本相比之下反而效率很不錯，主要原因是email數據不夠復雜，僅通過前幾位就可以比較出結果。如果每行數據比較長，而且很多行要到后幾個字符才能比較出來，肯定就不那么快了。

hash值的計算雖然執行了一系列乘法，不過還是相當迅速。

D語言版本執行了hash值和字符串比較，是比較完善的，效率很不錯。C＋＋相應版本看來要提高set的效率才能達到。

jzhang的第一個python版本在我的機器上執行如下：
lijie t # python test2.py
3122.9569912 ms
lijie t # python test2.py
3209.42997932 ms
lijie t # python test2.py
3141.47305489 ms
lijie t # python test2.py
3129.57286835 ms
lijie t # python test2.py
3196.03514671 ms

我做了點修改，執行速度提高了一些：
#remove?duplicated?email?address?from?file
import?datetime
from?time?import?time
if?__name__?==?"__main__":
?start?=?time()
?hashtable?=?{}
?f?=?file("email.txt","r")
?f2?=?file("email_new.txt","w")
?for?line?in?f.xreadlines():
??if?not?hashtable.has_key(line):
???hashtable[line]?=?1
???f2.write(line)
?f.close()
?f2.close()
?print?(time()?-?start)?*?1000,?"ms"
在我的機器上執行結果如下：
lijie t # python test1.py
2239.22801018 ms
lijie t # python test1.py
2301.00703239 ms
lijie t # python test1.py
2282.06086159 ms
lijie t # python test1.py
2296.57006264 ms
lijie t # python test1.py
2281.25810623 ms

不過還是沒有m網友的效率高。

在F版本的基礎上，借鑒m網友的做法，實現一個G版本：

G、排序并去除重復元素，比較hash和字符串版本：
#include?<iostream>
#include?<string>
#include?<fstream>
#include?<iterator>
#include?<sys/time.h>
#include?<vector>
using?namespace?std;


size_t?my_hash?(const?char*?str)
{
????????size_t?ret?=?0;
????????while?(*str)
????????????????ret?=?11?*?ret?+?*str++;
????????return?ret;
}

class?Email
{
private:
????????size_t?hash;
????????const?char*?mail;
????????friend?bool?operator?<?(const?Email&?lhs,?const?Email&?rhs);
public:
????????Email?(const?char*?mail_)
????????????????:?hash(my_hash(mail_)),?mail(mail_)
????????{
????????}

????????bool?operator?==?(const?Email&?rhs)
????????{
????????????????if?(hash?==?rhs.hash)
????????????????????????return?strcmp(mail,?rhs.mail)?==?0;
????????????????return?false;
????????}

????????const?char*?getEmail()const
????????{
????????????????return?mail;
????????}
};

bool?operator?<?(const?Email&?lhs,?const?Email&?rhs)
{
????????if?(lhs.hash?==?rhs.hash)
????????????????return?strcmp(lhs.mail,?rhs.mail)?<?0;
????????return?lhs.hash?<?rhs.hash;
}

int?main(int?argc,?char**?argv)
{
????????if?(argc?<?3)
????????{
????????????????cout?<<?"Wrong?arguments"?<<?endl;
????????????????return?1;
????????}

????????FILE*?fin?=?fopen(argv[1],?"r");
????????if?(!fin)
????????{
????????????????cout?<<?"Invalid?input?file"?<<?endl;
????????????????return?2;
????????}
????????FILE*?fout?=?fopen(argv[2],?"w");
????????if?(!fout)
????????{
????????????????fclose(fin);
????????????????cout?<<?"Invalid?output?file"?<<?endl;
????????????????return?3;
????????}

????????timeval?start,?end;

????????const?int?BUF_SIZE?=?20?*?1024?*?1024;
????????char*?buffer?=?new?char[BUF_SIZE];
????????memset(buffer,?0,?BUF_SIZE);

????????gettimeofday(&start,?0);
????????vector<Email>?emails;

????????size_t?read?=?fread?(buffer,?BUF_SIZE,?1,?fin);
????????char*?begin?=?buffer;
????????char*?current?=?buffer;

????????while?(*current?!=?'\0')
????????{
????????????????if?(*current?==?'\n')
????????????????{
????????????????????????*current?=?'\0';
????????????????????????emails.push_back(begin);
????????????????????????begin?=?current?+?1;
????????????????}
????????????????++?current;
????????}
????????fclose(fin);
????????sort(emails.begin(),?emails.end());
????????emails.erase?(unique(?emails.begin(),?emails.end()?),?emails.end());

????????for?(vector<Email>::const_iterator?iter?=?emails.begin();
?????????????iter?!=?emails.end();
?????????????iter?++)
????????{
????????????????fputs((*iter).getEmail(),?fout);
????????????????fwrite("\n",?1,?1,?fout);
????????}

????????fclose(fout);

????????gettimeofday(&end,?0);

????????printf("Time?used:?%d?ms\n",?((end.tv_sec?-?start.tv_sec)?*?1000?+?(end.tv_usec?-?start.tv_usec)?/?1000));

????????delete[]?buffer;

????????return?0;
}

在我的機器上執行如下：
lijie t # ./test7 email.txt email-new.txt
Time used: 676 ms
lijie t # ./test7 email.txt email-new.txt
Time used: 675 ms
lijie t # ./test7 email.txt email-new.txt
Time used: 671 ms
lijie t # ./test7 email.txt email-new.txt
Time used: 669 ms
lijie t # ./test7 email.txt email-new.txt
Time used: 673 ms

比F版本快了2倍，也快過了其它所有版本。不過由于數據是vector保存的，在數據大量重復的情況下，性能可能會有較大的降低。

把operator<和operator==的實現改為strcmp比較，執行結果如下：
lijie t # ./test8 email.txt email-new.txt
Time used: 1275 ms
lijie t # ./test8 email.txt email-new.txt
Time used: 1267 ms
lijie t # ./test8 email.txt email-new.txt
Time used: 1297 ms
lijie t # ./test8 email.txt email-new.txt
Time used: 1296 ms
lijie t # ./test8 email.txt email-new.txt
Time used: 1271 ms

修改了下，增加了計時，修正了fread使用錯誤。

#include?<iostream>
#include?<string>
#include?<fstream>
#include?<iterator>
#include?<vector>
using?namespace?std;

#ifdef?_WIN32
#?include?<windows.h>
#else?//?_WIN32
#?include?<sys/time.h>
#endif?//?_WIN32


size_t?my_hash?(const?char*?str)
{
????????size_t?ret?=?0;
????????while?(*str)
????????????????ret?=?11?*?ret?+?*str++;
????????return?ret;
}

class?Email
{
private:
????????size_t?hash;
????????const?char*?mail;
????????friend?bool?operator?<?(const?Email&?lhs,?const?Email&?rhs);
public:
????????Email?(const?char*?mail_)
????????????????:?hash(my_hash(mail_)),?mail(mail_)
????????{
????????}

????????bool?operator?==?(const?Email&?rhs)
????????{
????????????????if?(hash?==?rhs.hash)
????????????????????????return?strcmp(mail,?rhs.mail)?==?0;
????????????????return?false;
????????}

????????const?char*?getEmail()const
????????{
????????????????return?mail;
????????}
};

bool?operator?<?(const?Email&?lhs,?const?Email&?rhs)
{
????????if?(lhs.hash?==?rhs.hash)
????????????????return?strcmp(lhs.mail,?rhs.mail)?<?0;
????????return?lhs.hash?<?rhs.hash;
}

#ifndef?_WIN32
class?Timer
{
????????timeval?begin,?end;
public:
????????void?start?()?{gettimeofday(&begin,?0);}
????????void?stop?()?{gettimeofday(&end,?0);}
????????size_t?milliseconds?()?const?{
????????????????return?(end.tv_sec?-?begin.tv_sec)?*?1000?+?(end.tv_usec?-?begin.tv_usec)?/?1000;
????????}
};
#else?//?_WIN32
class?Timer
{
????????DWORD?begin,?end;
public:
????????void?start?()?{begin?=?GetTickCount();}
????????void?stop?()?{end?=?GetTickCount();}
????????size_t?milliseconds?()?const?{
????????????????return?end?-?begin;
????????}
};
#endif?//?_WIN32


int?main(int?argc,?char**?argv)
{
????????if?(argc?<?3)
????????{
????????????????cout?<<?"Wrong?arguments"?<<?endl;
????????????????return?1;
????????}

????????for?(int?i=0;?i<10;?++i)?{

???????FILE*?fin?=?fopen(argv[1],?"r");
????????if?(!fin)
????????{
????????????????cout?<<?"Invalid?input?file"?<<?endl;
????????????????return?2;
????????}
????????FILE*?fout?=?fopen(argv[2],?"w");
????????if?(!fout)
????????{
????????????????fclose(fin);
????????????????cout?<<?"Invalid?output?file"?<<?endl;
????????????????return?3;
????????}

????????Timer?total,?part;
????????total.start();
????????part.start();

????????const?int?BUF_SIZE?=?20?*?1024?*?1024;

????????char*?buffer?=?new?char[BUF_SIZE];
????????if?(!buffer){
????????????????//?cout?<<?"Alloc?buffer?failed"?<<?endl;
????????????????return?4;
????????}

????????part.stop();
????????//?cout?<<?"Alloc?buffer,?"?<<?part.milliseconds()?<<?"?ms?used."?<<?endl;
????????part.start();

????????size_t?read?=?fread?(buffer,?1,?BUF_SIZE,?fin);
????????fclose(fin);
????????buffer[read]?=?'\0';
????????part.stop();
????????//?cout?<<?"Read?file,?"?<<?part.milliseconds()?<<?"?ms?used."?<<?endl;
????????part.start();

????????vector<Email>?emails;

????????char*?begin?=?buffer;
????????char*?current?=?buffer;

????????while?(*current?!=?'\0')
????????{
????????????????if?(*current?==?'\n')
????????????????{
????????????????????????*current?=?'\0';
????????????????????????emails.push_back(begin);
????????????????????????begin?=?current?+?1;
????????????????}
????????????????++?current;
????????}

????????part.stop();
????????//?cout?<<?"Put?emails?into?vector,?"?<<?part.milliseconds()?<<?"?ms?used."?<<?endl;
????????part.start();

????????sort(emails.begin(),?emails.end());
????????part.stop();
????????//?cout?<<?"Sort?emails,?"?<<?part.milliseconds()?<<?"?ms?used."?<<?endl;
????????part.start();

????????emails.erase?(unique(?emails.begin(),?emails.end()?),?emails.end());
????????part.stop();
????????//?cout?<<?"Unique?emails,?"?<<?part.milliseconds()?<<?"?ms?used."?<<?endl;
????????part.start();

????????for?(vector<Email>::const_iterator?iter?=?emails.begin();
?????????????iter?!=?emails.end();
?????????????iter?++)
????????{
????????????????fputs((*iter).getEmail(),?fout);
????????????????fwrite("\n",?1,?1,?fout);
????????}

????????fclose(fout);

????????part.stop();
????????//?cout?<<?"Write?emails?into?new?file,?"?<<?part.milliseconds()?<<?"?ms?used."?<<?endl;

????????total.stop();

????????cout?<<?"Total?used:?"?<<?total.milliseconds()?<<?"?ms."?<<?endl;

????????delete[]?buffer;
????????}

????????return?0;
}

使用“-O3 -fomit-frame-pointer -funroll-loops -mtune=pentium4”選項編譯，耗時從680ms減少到620ms

優化文件讀寫版：
#include?<iostream>
#include?<string>
#include?<fstream>
#include?<iterator>
#include?<vector>
using?namespace?std;

//?config
#define?USE_CACHE
//#define?PROFILE
//?end?config


#ifdef?_WIN32
#?include?<windows.h>
#else?//?_WIN32
#?include?<sys/time.h>
#endif?//?_WIN32

#ifndef?_WIN32
class?Timer
{
????timeval?begin,?end;
public:
????void?start?()?{gettimeofday(&begin,?0);}
????void?stop?()?{gettimeofday(&end,?0);}
????size_t?milliseconds?()?const?{
????????return?(end.tv_sec?-?begin.tv_sec)?*?1000?+?(end.tv_usec?-?begin.tv_usec)?/?1000;
????}
};
#else?//?_WIN32
class?Timer
{
????DWORD?begin,?end;
public:
????void?start?()?{begin?=?GetTickCount();}
????void?stop?()?{end?=?GetTickCount();}
????size_t?milliseconds?()?const?{
????????return?end?-?begin;
????}
};
#endif?//?_WIN32


#ifdef?PROFILE
#?define?PROFILE_OUTPUT(timer,info)?\
????timer.stop();?\
????cout?<<?info?<<?":?"?<<?timer.milliseconds()?<<?"?ms?used."?<<?endl;?\
????timer.start()
#else?//?PROFILE
#?define?PROFILE_OUTPUT(timer,info)
#endif?//?PROFILE



size_t?my_hash?(const?char*?str)
{
????size_t?ret?=?0;
????while?(*str)
????????????ret?=?11?*?ret?+?*str++;
????return?ret;
}

class?Email
{
private:
????size_t?hash;
????const?char*?mail;
????friend?bool?operator?<?(const?Email&?lhs,?const?Email&?rhs);
public:
????Email?(const?char*?mail_)
????????:?hash(my_hash(mail_)),?mail(mail_)
????{
????}

????bool?operator?==?(const?Email&?rhs)
????{
????????if?(hash?==?rhs.hash)
????????????return?strcmp(mail,?rhs.mail)?==?0;
????????return?false;
????}

????const?char*?getEmail()?const
????{
????????return?mail;
????}

????size_t?getLength()?const
????{
????????return?strlen(mail);
????}
};

bool?operator?<?(const?Email&?lhs,?const?Email&?rhs)
{
????if?(lhs.hash?==?rhs.hash)
????????return?strcmp(lhs.mail,?rhs.mail)?<?0;
????return?lhs.hash?<?rhs.hash;
}



#ifdef?USE_CACHE
class?OfstreamBuffer
{
????ofstream&?ofs;
????size_t?buf_size;
????size_t?offset;
????char*?buffer;

public:
????OfstreamBuffer?(ofstream&?ofs_,?size_t?buf_size_)
????????:?ofs(ofs_),?buf_size(buf_size_),?offset(0)
????{
????????buffer?=?new?char[buf_size_];
????}

????~OfstreamBuffer?()
????{
????????flush();
????????delete[]?buffer;
????}

????void?write?(const?char*?ptr,?size_t?size)
????{
????????while?(size?>?0)
????????{
????????????size_t?copy_size?=?buf_size?-?offset;
????????????if?(copy_size?>?size)
????????????????copy_size?=?size;
????????????memcpy?(buffer?+?offset,?ptr,?copy_size);
????????????offset?+=?copy_size;
????????????ptr?+=?copy_size;
????????????size?-=?copy_size;

????????????if?(offset?==?buf_size)
????????????????flush?();
????????}
????}

????void?flush?()
????{
????????if?(offset?>?0)
????????{
????????????ofs.write(buffer,?offset);
????????????offset?=?0;
????????}
????????ofs.flush();
????}
};
#else//?USE_CACHE
class?OfstreamBuffer
{
????ofstream&?ofs;

public:
????OfstreamBuffer?(ofstream&?ofs_,?size_t?buf_size_)
????????:?ofs(ofs_)
????{
????}

????void?write?(const?char*?ptr,?size_t?size)
????{
????????ofs.write(ptr,?size);
????}

????void?flush?()
????{
????????ofs.flush();
????}
};
#endif?//?USE_CACHE




int?main(int?argc,?char**?argv)
{
????if?(argc?<?3)
????{
????????cout?<<?"Wrong?arguments"?<<?endl;
????????return?1;
????}

????for?(int?i=0;?i<1;?++i)?{

????????ifstream?ifs(argv[1],?ios::binary);
????????if?(!ifs)
????????{
????????????cout?<<?"Invalid?input?file"?<<?endl;
????????????return?2;
????????}

????????ofstream?ofs(argv[2],?ios::binary);
????????if?(!ofs)
????????{
????????????cout?<<?"Invalid?output?file"?<<?endl;
????????????return?3;
????????}

????????Timer?total,?part;
????????total.start();
????????part.start();

????????ifs.seekg(0,?ios_base::end);
????????size_t?file_size?=?(size_t)ifs.tellg()?+?1;
????????cout?<<?"file?size:?"?<<?file_size?<<?endl;
????????ifs.seekg(0,?ios_base::beg);

????????char*?buffer?=?new?char[file_size];
????????if?(!buffer){
????????????cout?<<?"Alloc?buffer?failed"?<<?endl;
????????????return?4;
????????}

????????PROFILE_OUTPUT(part,?"Alloc?buffer");

????????ifs.read(buffer,?file_size);
????????buffer[file_size]?=?'\0';

????????PROFILE_OUTPUT(part,?"Read?file");

????????vector<Email>?emails;
????????emails.reserve(1000000);

????????char*?begin?=?buffer;
????????char*?current?=?buffer;

????????while?(*current?!=?'\0')
????????{
????????????if?(*current?==?'\n')
????????????{
????????????????*current?=?'\0';
????????????????emails.push_back(begin);
????????????????begin?=?current?+?1;
????????????}
????????????++?current;
????????}

????????PROFILE_OUTPUT(part,?"Put?emails?into?vector");

????????sort(emails.begin(),?emails.end());

????????PROFILE_OUTPUT(part,?"Sort?emails");

????????emails.erase?(unique(?emails.begin(),?emails.end()?),?emails.end());

????????PROFILE_OUTPUT(part,?"Unique?emails");

????????OfstreamBuffer?ofsBuffer?(ofs,?4?*?1024);

????????for?(vector<Email>::const_iterator?iter?=?emails.begin();
?????????????iter?!=?emails.end();
?????????????iter?++?)
????????{
????????????ofsBuffer.write(iter->getEmail(),?iter->getLength());
????????????ofsBuffer.write("\n",?1);
????????}
????????ofsBuffer.flush();

????????PROFILE_OUTPUT(part,?"Write?emails?into?new?file");

????????total.stop();
????????cout?<<?"Total?used:?"?<<?total.milliseconds()?<<?"?ms."?<<?endl;


????????delete[]?buffer;
????}

????return?0;
}
這個版本在windows上用dev-cpp所帶的gcc 3.4.2來編譯，最好成績是609ms。在cygwin里可以達到650ms。
posted on 2006-04-03 11:00 qiezi 閱讀(2811) 評論(27)  編輯 收藏 引用 所屬分類: C＋＋ 、雜談
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