本文主要是介绍用正向和逆向最大匹配算法进行中文分词，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1.概述
用正向和逆向最大匹配算法进行中文分词。
2.遇到的问题
编码问题，Linux默认的编码是UTF-8编码，对于汉字，每个字占三个字节。而本文使用的语料为1998年1月的人民日报语料，为GB2312编码，每个汉字占两个字节。
本文所用的Ubuntu Linux操作系统默认是不支持GB2312等中文编码的，因此需要对系统添加GB2312编码的支持。添加方式参见：
3.分词结果
分词结果如下图所示：
从图中可以看出，逆向最大匹配分词的准确率和召回率均大于正向最大匹配分词方法，但是幅度相差不是很大。
4.源代码
源代码分为三个文件：
segmentutil.cpp（对语料进行预处理），它是单独运行的，可以将原始语料制作成词典文件和测试文件。
dictionary.h（词典头文件，初始化词典）和main.cpp（进行分词操作）这两个文件需要一起编译运行。可以对测试文件进行分词，该过程需要用到前面文件生成的词典文件和测试文件。
（1）segmentutil.cpp（对语料进行预处理）
#include <string>
#include <iostream>
#include <fstream>
#include <cstdlib>using namespace std;/** 工具类* 功能：进行各种字符串操作、语料预处理操作* 含有2个字符串操作的函数 * 含有5个语料预处理相关的函数 */
class SegmentUtil{public:string removeLetters(string str_in); //去掉字符串中的英文字母string& replace_all(string &str, string old_str, string new_str); //置换字符串的特定字串void removeNum(); //去掉语料中的编号void spareLine(); //将语料进行分行void spareFile(); //将语料分为词典和测试语料void makeDict(); //构造词典void makeDict_2(); //构造词典
};/** 函数功能：删除词性标记（即去掉字符串中的英文字母）* 函数输入：含有词性标记的字符串* 函数输出：不含词性标记的字符串*/
string SegmentUtil::removeLetters(string str_in){char s[10000];int j = 0;for(int i = 0; i < str_in.length(); i++){if(!(str_in[i] >= 'a' && str_in[i] <= 'z' || str_in[i] >= 'A' && str_in[i] <= 'Z')){s[j] = str_in[i];j++; }}s[j] = '\0';string str_out = s;return str_out;
}/** 函数功能：将字符串中的所有特定子串置换为新的字符串* 函数输入：str 需要进行操作的字符串* old_str 旧的字符串* new_str 新的字符串* 函数输出：置换完毕的字符串*/
string& SegmentUtil::replace_all(string &str, string old_str, string new_str){while(1){string::size_type pos(0);if((pos = str.find(old_str)) != string::npos){str.replace(pos, old_str.length(), new_str);}else{break;}}return str;
}/** 函数功能：去掉语料中每各段落前的编号* 函数输入：待处理的文件* 函数输出：处理完的文件*/
void SegmentUtil::removeNum(){ifstream fin("199801_1.txt");if(!fin){cerr << "removeNum : Unable open input file !" << endl;exit(-1);}ofstream fout("199801_2.txt");if(!fout){cerr << "removeNum : Unable open output file !" << endl;exit(-1);}string str_in = "";string str_out = "";while(getline(fin, str_in, '\n')){if(str_in.find('/') == 18){str_out = str_in.substr(22, str_in.length() - 22);}fout << str_out << endl;}fin.close();fout.close();
}/** 函数功能：将语料进行分行* 函数输入：待处理的文件，文件中多个句子在一个段落中，每个段落为一行* 函数输出：处理完的文件，每个句子为一行*/
void SegmentUtil::spareLine(){ifstream fin("199801_2.txt");if(!fin){cerr << "makeLine : Unable open input file !" << endl;exit(-1);}ofstream fout("199801_3.txt");if(!fout){cerr << "makeLine : Unable open output file !" << endl;exit(-1);}string str_in = "";string str_out = "";while(getline(fin, str_in, '\n')){if(str_in.find('/') == 18){str_out = str_in.substr(22, str_in.length() - 22);}fout << str_out << endl;}fin.close();fout.close();
}/** 函数功能：按照一定的比例，将原始语料分为词典语料和测试语料，默认比例为9：1。* 函数输入：分好行的语料文件，每个句子为一行* 函数输出：两个文件，文件1用于构造词典，文件2用于测试*/
void SegmentUtil::spareFile(){ifstream fin("199801_003.txt");if(!fin){cerr << "spareLine : Unable open input file !" << endl;exit(-1);}ofstream fout_1("dict_1.txt");if(!fout_1){cerr << "spareLine : Unable open output file : dict.txt !" << endl;exit(-1);}ofstream fout_2("test.txt");if(!fout_2){cerr << "spareLine : Unable open output file : test.txt !" << endl;exit(-1);}long count = 0;string str_in = "";string str_out = "";while(getline(fin, str_in, '\n')){//过滤掉词性标记，即英文字母str_out = removeLetters(str_in);//以句子为单位，将语料按比例分为两个文件if(count % 10 == 0){fout_2 << str_out << endl;}else{fout_1 << str_out << endl;}count++;}fin.close();fout_1.close();fout_2.close();
}/** 函数功能：构造词典，使每个词语为一行* 函数输入：分好行的语料文件，每个句子为一行* 函数输出：初步的词典文件，每个词语为一行，但可能有空行*/
void SegmentUtil::makeDict(){ifstream fin("dict_1.txt");if(!fin){cerr << "makeDict : Unable open input file !" << endl;exit(-1);}ofstream fout("dict_2.txt");if(!fout){cerr << "makeDict : Unable open output file !" << endl;exit(-1);}string line = "";while(getline(fin, line, '\n')){//将分词标记（/）和中文标点置换为回车for(int i = 0; i < line.length(); i++){unsigned char ch = (unsigned char) line[i];if(ch == '/'){line[i] = '\n'; }}line = replace_all(line, "，", "\n");line = replace_all(line, "。", "\n");line = replace_all(line, "？", "\n");line = replace_all(line, "！", "\n");line = replace_all(line, "《", "\n");line = replace_all(line, "》", "\n");line = replace_all(line, "”", "\n");line = replace_all(line, "“", "\n");line = replace_all(line, "：", "\n");line = replace_all(line, "、", "\n");line = replace_all(line, "（", "\n");line = replace_all(line, "）", "\n");line = replace_all(line, "[", "\n");line = replace_all(line, "]", "\n");fout << line << endl;}fin.close();fout.close();
}/** 函数功能：构造词典，使每个词语为一行（去掉词典中的空行）* 函数输入：初步的词典文件，每个词语为一行，但可能有空行* 函数输出：最终的语料文件，每个词语为一行，去掉了空行*/
void SegmentUtil::makeDict_2(){ifstream fin("dict_2.txt");if(!fin){cerr << "makeDict_2 : Unable open input file !" << endl;exit(-1);}ofstream fout("dict_3.txt");if(!fout){cerr << "makeDict_2 : Unable open output file !" << endl;exit(-1);}string line = "";//去掉空行while(getline(fin, line, '\n')){if(!line.empty()){fout << line << endl;}}fin.close();fout.close();
}int main(){SegmentUtil seg;//1.将原始语料分为词典语料和测试语料seg.spareFile();//2.构造词典seg.makeDict();seg.makeDict_2();
}（2）dictionary.h（词典头文件，初始化词典）
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <set>
#include <cstdlib>using namespace std;class Dictionary{private:string strline; //保存每行内容string word; //保存一个词语set<string> word_set; //词典，用集合表示public:Dictionary(); //构造函数，初始化词典~Dictionary();int findWord(string word); //在词典中查找特定的词语
};Dictionary::Dictionary(){//读取词典文件fstream fin("dict_3.txt");if(!fin){cerr << "open file error !" << endl;exit(-1);}//将每个词语加入集合while(getline(fin, strline, '\n')){istringstream istr(strline);istr >> word; //word_set.insert(word); //}
}Dictionary::~Dictionary(){}int Dictionary::findWord(string word){if(word_set.find(word) != word_set.end()){return 1;} else {return 0;}
}
（3）main.cpp（进行分词操作）
#include <cstdlib>
#include "dictionary.h"
#include <vector>
#include <iomanip>
#include <map>const int MaxWordLength = 10; //最大词长为10个字节（即5个汉字）
const char Separator = '/'; //词界标记Dictionary word_dict; //初始化一个词典/** 函数功能：对字符串用最大匹配算法（正向）处理* 函数输入：汉字字符串* 函数输出：分好词的字符串*/
string SegmentSentence_1(string s1){string s2 = ""; //用s2存放分词结果while(!s1.empty()){int len = s1.length(); //取输入串长度if(len > MaxWordLength){len = MaxWordLength; //只在最大词长范围内进行处理}string w = s1.substr(0, len);int n = word_dict.findWord(w); //在词典中查找相应的词while(len > 2 && n == 0){len -= 2; //从候选词右边减掉一个汉字，将剩下的部分作为候选词w = s1.substr(0, len);n = word_dict.findWord(w);}s2 = s2 + w + Separator;s1 = s1.substr(w.length(), s1.length() - w.length());}return s2;
}/** 函数功能：对字符串用最大匹配算法（逆向）处理* 函数输入：汉字字符串* 函数输出：分好词的字符串*/
string SegmentSentence_2(string s1){string s2 = ""; //用s2存放分词结果while(!s1.empty()){int len = s1.length(); //取输入串长度if(len > MaxWordLength){len = MaxWordLength; //只在最大词长范围内进行处理}string w = s1.substr(s1.length() - len, len);int n = word_dict.findWord(w); //在词典中查找相应的词while(len > 2 && n == 0){len -= 2; //从候选词左边减掉一个汉字，将剩下的部分作为候选词w = s1.substr(s1.length() - len, len);n = word_dict.findWord(w);}w = w + Separator;s2 = w + s2;s1 = s1.substr(0, s1.length() - len);}return s2;
}/** 函数功能：对句子进行最大匹配法处理，包含对特殊字符的处理* 函数输入：1.含有汉字、英文符号的字符串* 2.flag=1调用正向最大匹配算法，flag=2调用逆向最大匹配算法* 函数输出：分好词的字符串*/
string SegmentSentenceMM(string s1, int flag){string s2 = ""; //用s2存放分词结果int i;int dd;while(!s1.empty()){unsigned char ch = (unsigned char)s1[0];if(ch < 128){//处理西文字符i = 1;dd = s1.length();while(i < dd && ((unsigned char)s1[i] < 128) && (s1[i] != 10) && (s1[i] != 13)){//s1[i]不能是换行符或回车符i++;}//中止循环条件：出现中文字符、换行或者回车if(i == 1 && (ch == 10 || ch == 13)){//如果是换行或回车符，将它拷贝给s2输出s2 += s1.substr(0, i);}else{s2 += s1.substr(0, i) + Separator;}s1 = s1.substr(i, dd);continue;}else{if(ch < 176){//中文标点等非汉字字符i = 0;dd = s1.length();//获取中文双字节特殊字符（非汉字、非中文标点），中止循环条件：超过长度、出现中文标点符号、出现汉字while(i < dd && ((unsigned char)s1[i] < 176) && ((unsigned char)s1[i] >= 161)&& (!((unsigned char)s1[i] == 161 && ((unsigned char)s1[i+1] >= 162 && (unsigned char)s1[i+1] <= 168)))&& (!((unsigned char)s1[i] == 161 && ((unsigned char)s1[i+1] >= 171 && (unsigned char)s1[i+1] <= 191)))&& (!((unsigned char)s1[i] == 163 && ((unsigned char)s1[i+1] == 161 || (unsigned char)s1[i+1] == 168|| (unsigned char)s1[i+1] == 169 || (unsigned char)s1[i+1] == 172 || (unsigned char)s1[i+1] == 186 || (unsigned char)s1[i+1] == 187 || (unsigned char)s1[i+1] == 191)))){//假定没有半个汉字i = i + 2;}//出现中文标点if(i == 0){i = i + 2;}//中文标点每个加一个分词标记；其他非汉字双字节字符连续输出，只加一个分词标记s2 += s1.substr(0, i) + Separator;s1 = s1.substr(i, dd);continue;}}//以下处理汉字串i = 2;dd = s1.length();while(i < dd && (unsigned char)s1[i] >= 176){i += 2;}if(flag == 1){//调用正向最大匹配s2 += SegmentSentence_1(s1.substr(0, i));}else{//调用逆向最大匹配s2 += SegmentSentence_2(s1.substr(0, i));}s1 = s1.substr(i, dd); }return s2;
}/** 函数功能：删除分词标记（即去掉字符串中的/）* 函数输入：含有分词标记的字符串* 函数输出：不含分词标记的字符串*/
string removeSeparator(string str_in){char s[10000];int j = 0;for(int i = 0; i < str_in.length(); i++){if(!(str_in[i] == '/')){s[j] = str_in[i];j++;}}s[j] = '\0';string str_out = s;return str_out;
}/** 函数功能：计算切分标记的位置* 函数输入：1.strline_in未进行切分的汉字字符串2.strline_right进行切分后的汉字字符串* 函数输出：vecetor，其中存放了strline_in中哪些位置放置了分词标记* 注意：vector中不包含最后标记的位置，但是包含位置0。*/
vector<int> getPos(string strline_right, string strline_in){int pos_1 = 0;int pos_2 = -1;int pos_3 = 0;string word = "";vector<int> vec;int length = strline_right.length();while(pos_2 < length){//前面的分词标记pos_1 = pos_2;//后面的分词标记pos_2 = strline_right.find('/', pos_1 + 1);if(pos_2 > pos_1){//将两个分词标记之间的单词取出word = strline_right.substr(pos_1 + 1, pos_2 - pos_1 - 1);//根据单词去输入序列中查出出现的位置pos_3 = strline_in.find(word, pos_3);//将位置存入数组vec.push_back(pos_3);pos_3 = pos_3 + word.size();}else{break;}}return vec;
}/** 函数功能：获取单个句子切分的结果统计* 函数输入：1.vec_right 正确的分词标记位置集合* 2.vec_out 函数切分得到的分词标记位置集合* 函数输出：返回一个veceor，含有两个元素* 1.不该切分而切分的数量* 2.该切分而未切分的数量*/
vector<int> getCount(vector<int> vec_right, vector<int> vec_out){vector<int> vec; //存放计算结果map<int, int> map_result;int length_1 = 0; //map改变前的长度int length_2 = 0; //map改变后的长度int count_1 = 0; //不该切分而切分的数量int count_2 = 0; //该切分而未切分的数量for(int i = 0; i < vec_right.size(); i++){map_result[vec_right[i]] = 0;}length_1 = map_result.size();for(int i = 0; i < vec_out.size(); i++){++map_result[vec_out[i]];}length_2 = map_result.size();count_1 = length_2 - length_1;for(int i = 0; i < vec_right.size(); i++){if(map_result[vec_right[i]] == 0){++count_2;}}vec.push_back(count_1);vec.push_back(count_2);return vec;
}/** 主函数：进行分词并统计分词结果****/
int main(int argc, char *argv[]){string strline_right; //输入语料：用作标准分词结果string strline_in; //去掉分词标记的语料（用作分词的输入）string strline_out_1; //正向最大匹配分词完毕的语料string strline_out_2; //逆向最大匹配分词完毕的语料ifstream fin("test.txt"); //打开输入文件if(!fin){cout << "Unable to open input file !" << argv[1] << endl;exit(-1);}ofstream fout("result.txt"); //确定输出文件if(!fout){cout << "Unable to open output file !" << endl;exit(-1);}long count = 0; //句子编号long count_right_all = 0; //准确的切分总数long count_out_1_all = 0; //正向匹配切分总数long count_out_2_all = 0; //逆向匹配切分总数long count_out_1_right_all = 0; //正向匹配切分正确总数long count_out_2_right_all = 0; //逆向匹配切分正确总数while(getline(fin, strline_right, '\n')){if(strline_right.length() > 1){//去掉分词标记strline_in = removeSeparator(strline_right);//正向最大匹配分词strline_out_1 = strline_right;strline_out_1 = SegmentSentenceMM(strline_in, 1);//逆向最大匹配分词strline_out_2 = strline_right;strline_out_2 = SegmentSentenceMM(strline_in, 2);//输出结果count++;cout << "----------------------------------------------" << endl;cout << "句子编号：" << count << endl;cout << endl;cout << "待分词的句子长度: " << strline_in.length() << " 句子：" << endl;cout << strline_in << endl;cout << endl;cout << "标准比对结果长度: " << strline_right.length() << " 句子：" << endl;cout << strline_right << endl;cout << endl;cout << "正向匹配分词长度: " << strline_out_1.length() << " 句子：" << endl;cout << strline_out_1 << endl;cout << endl;cout << "逆向匹配分词长度: " << strline_out_2.length() << " 句子：" << endl;cout << strline_out_2 << endl;cout << endl;//计算准确率、召回率//Rev()vector<int> vec_right = getPos(strline_right, strline_in);vector<int> vec_out_1 = getPos(strline_out_1, strline_in);vector<int> vec_out_2 = getPos(strline_out_2, strline_in);cout << "标准结果：" << endl;for(int i = 0; i < vec_right.size(); i++){cout << setw(4) << vec_right[i];}cout << endl;cout << "正向匹配结果：" << endl;for(int i = 0; i < vec_out_1.size(); i++){cout << setw(4) << vec_out_1[i];}cout << endl;cout << "逆向匹配结果：" << endl;for(int i = 0; i < vec_out_2.size(); i++){cout << setw(4) << vec_out_2[i];}cout << endl;vector<int> vec_count_1 = getCount(vec_right, vec_out_1);vector<int> vec_count_2 = getCount(vec_right, vec_out_2);//准确的切分数量int count_right = vec_right.size();//切分得到的数量int count_out_1 = vec_out_1.size();int count_out_2 = vec_out_2.size();//切分正确的数量int count_out_1_right = count_out_1 - vec_count_1[0] - vec_count_1[1];int count_out_2_right = count_out_2 - vec_count_2[0] - vec_count_2[1];cout << "正向最大匹配：" << endl; cout << " 不该切分而切分的数量：" << vec_count_1[0] << endl;cout << " 该切分而未切分的数量：" << vec_count_1[1] << endl;cout << "逆向最大匹配：" << endl; cout << " 不该切分而切分的数量：" << vec_count_2[0] << endl;cout << " 该切分而未切分的数量：" << vec_count_2[1] << endl;count_right_all += count_right;count_out_1_all += count_out_1;count_out_2_all += count_out_2;count_out_1_right_all += count_out_1_right;count_out_2_right_all += count_out_2_right;}}double kk_1 = (double)count_out_1_right_all / count_out_1_all; //正向准确率double kk_2 = (double)count_out_1_right_all / count_right_all; //正向召回率double kk_3 = (double)count_out_2_right_all / count_out_2_all; //逆向准确率double kk_4 = (double)count_out_2_right_all / count_right_all; //逆向召回率cout << "----------------------------------" << endl;cout << endl;cout << "统计结果：" << endl;cout << "正向准确率：" << kk_1*100 << "% 正向召回率：" << kk_2*100 << "%" << endl;cout << "逆向准确率：" << kk_3*100 << "% 逆向召回率：" << kk_4*100 << "%" << endl;return 0;
}
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