Boyer-Moore算法的C++实现
以上给出了通俗易懂的算法讲解，下面给出代码实现，使用的宽字符，这样就不限于英文字母了:(stdafx.h编译不过去就屏蔽掉)
// StringSearch_BoyerMoore.cpp : 定义控制台应用程序的入口点。
//
/*
@Date: 2016/03/21 18:31;
@Where: Tongzhou District of Beijing;
@Author: Alex Hong;
@Mail: worksdata@163.com;
@Reference:
http://www.ruanyifeng.com/blog/2013/05/boyer-moore_string_search_algorithm.html BM算法-阮一峰的网络日志;
*/
#include "stdafx.h"
#include <sstream>
#include <iostream>
#include <string>
#include <vector>
#include <map>
using namespace std;
typedef std::vector<int> TArrayInt;
TArrayInt g_arSearchResult;//store the index of searched result;
typedef std::map<std::wstring, int> TMapWszToInt; //E.g. "我,4":7;
typedef std::map<int, int> TMapIntToInt;
void StringSearch_BM(wchar_t* wszStrMain, int iLenMain, wchar_t* wszSearch, int iLenSearch, bool bOnlyFirst)
{
//reset variables;
g_arSearchResult.clear();
//handle exceptions..
if( NULL == wszStrMain || NULL == wszSearch)
return;
if(iLenSearch > iLenMain)
return;
/*
未知的字符有很多, 但是已知的搜索字符是有限的. 我们只初始化已知的字符的跳跃值(Skip), 数组中不存在的就是-1;
Shift数组的初始化同样基于这种想法.
初始化这两个数组的值后, 对于长主串/耗时的任务是有利的;
*/
int i = 0, j = 0;
//Initialize the Skip array data for Bad-Character-Rules..
TMapWszToInt mapSkip;
mapSkip.clear();
TMapWszToInt::iterator it1;
std::wostringstream oStream;
for(i = iLenSearch - 1; i > 0; --i)//0-->1;
{
for(j = i - 1; j >= 0; --j)
{
if(wszSearch[j] != wszSearch[i]) //Skip is for bad character which is different with wszSearch;
{
oStream.clear();//clear bad bits;
oStream.str(L"");//clear data;
oStream<<wszSearch[j]<<','<<i;//format to key string;
//wcout<<oStream.str().c_str()<<endl;//test..
it1 = mapSkip.find(oStream.str());
if(mapSkip.end() == it1) //only set the pos of nearest same bad character;
mapSkip.insert(TMapWszToInt::value_type(oStream.str(), i-j));
}
}
}
//好后缀的前提是: 至少有一个字符是相同的!!!!!!
//Initialize the Shift array data for Good-Suffix-Rules..
//Shift数组的键值是好后缀的最左字符的下标;
//1. 首先判断模式串中是否含有完全一致的好后缀;有就直接计算位移, EXIT;
// 其实这本身就是一个字符串搜索的过程,为了简化计算, 这里只使用Bad-Character-Rule;
//2. 如果没有, 就在串首寻找好后缀的子串;
TMapIntToInt mapShift;
mapShift.clear();
mapShift.insert(TMapIntToInt::value_type(0, iLenSearch));//0==i的话就匹配了, Shift[]=iLenSearch;
//1. try to find the same suffix..
for(int iSuffixPosL = iLenSearch - 1; iSuffixPosL > 0; --iSuffixPosL)//iSuffixPosL: left position of good suffix;
{
int iSuffixLen = iLenSearch - iSuffixPosL;
wchar_t* wszSuffix = wszSearch + iSuffixPosL;
for(int iPosMainL = iSuffixPosL - 1; iPosMainL >= 0;)//不断向左移动suffix串比较;
{
//compare..
for(i = 0; i < iSuffixLen; ++i)
{
if(wszSearch[iPosMainL+i] != wszSuffix[i])//bad character
break;
}
//check result..
if(iSuffixLen == i) //find it!
{
mapShift[iLenSearch-i] = iSuffixPosL - iPosMainL;
break; //结束为当前suffix找Shift值;
}
else //calc the skip distance;
{
for(j = i + 1; j < iSuffixLen; ++j)//在suffix中寻找最近的坏字符
{
if(wszSuffix[j] == wszSearch[iPosMainL+i])
break;
}
iPosMainL = iPosMainL - (j - i);//iSuffixLen==j的情况也适用;
}
}
}
//2. try to find the child suffix at head..
TMapIntToInt::iterator it2;
for(int iSuffixPosL = iLenSearch - 1; iSuffixPosL > 0; --iSuffixPosL)//iSuffixPosL: left position of good suffix;
{
it2 = mapShift.find(iSuffixPosL);
if(mapShift.end() == it2)
{
wchar_t* wszSuffix = NULL;
int iSuffixLen = 0;
for(i = 0; i < iLenSearch - iSuffixPosL; ++i)//form sub suffix big to small.
{
wszSuffix = wszSearch + iSuffixPosL + i;
iSuffixLen = iLenSearch - iSuffixPosL - i;
//compare if match..
for(j = 0; j < iSuffixLen; ++j)
{
if(wszSearch[j] != wszSuffix[j])
break;
}
if(iSuffixLen == j) //find it!
{
mapShift[iSuffixPosL] = iLenSearch - iSuffixLen; //以好后缀的最后一个字符为准;
break;
}
}
//if no sub suffix at all..
it2 = mapShift.find(iSuffixPosL);
if(mapShift.end() == it2)
mapShift[iSuffixPosL] = iLenSearch;
}
}
//================
//start to search!
//================
int iPosMainL = 0;//left iterator of main string;
//int iPosSearch = 0;//iterator of search string; no use!
while( iPosMainL <= iLenMain - iLenSearch + 1)
{
//compare with aligned sub-string..
int i = iLenSearch - 1;
for(; i >= 0; --i)//right to left comparison;
{
if(wszSearch[i] != wszStrMain[iPosMainL+i])//bad character!
break;
}
//----calc how many steps to move rightwards..----
int iSkip = 0;
if(i < 0)
{
g_arSearchResult.push_back(iPosMainL);
if(bOnlyFirst)
{
mapSkip.clear();
mapShift.clear();
return;
}
iSkip = iLenSearch;
}
else
{
//1. calc max skip steps for bad characters..
oStream.clear();//clear bits;
oStream.str(L"");//clear data;
oStream<<wszStrMain[iPosMainL+i]<<','<<i;
it1 = mapSkip.find((wchar_t*)oStream.str().c_str());
if(mapSkip.end() == it1)
iSkip = i + 1;
else
iSkip = it1->second;
}
//--2. calc max shift steps for good suffix..--
int iShift = 0;
if(i < iLenSearch - 1)//至少有一个相同的字符才可以使用"好后缀"规则!
{
it2 = mapShift.find(i-1);
if(mapShift.end() != it2)
iShift = it2->second;
}
iPosMainL += ((iSkip>iShift) ? iSkip : iShift);
}
//clear..
mapSkip.clear();
mapShift.clear();
}
int _tmain(int argc, _TCHAR* argv[])
{
wchar_t wszMainStr[] = L"THIS IS A 我你她我不是的LE EXA我们我们MPLEEXAMPLE我们";
wchar_t wszSearchStr[] = L"我们";
StringSearch_BM(wszMainStr, wcslen(wszMainStr), wszSearchStr, wcslen(wszSearchStr), false);
for(TArrayInt::iterator it = g_arSearchResult.begin(); it != g_arSearchResult.end(); ++it)
cout<<*it<<endl;
//clear..
g_arSearchResult.clear();
getchar();
return 0;
}
一些例子分析过程:
主字符串: THIS IS A SIMPLE EXAMPLE (长度:24)
搜索字符串: EXAMPLE (长度:7)
mapSkip的初始化值:
主串中的坏字符的下面字符是:'E'
mapSkip['L,6'] = 1
mapSkip['P,6'] = 2
mapSkip['M,6'] = 3
mapSkip['A,6'] = 4
mapSkip['X,6'] = 5
mapSkip['E,6'] = 不是坏字符, 舍去
其他: 7
-----------------------------------------------------------
搜索字符串: EXAMPLE (长度:7)
主串中的坏字符的下面字符是:
'L'
mapSkip['P,5'] = 1
mapSkip['M,5'] = 2
mapSkip['A,5'] = 3
mapSkip['X,5'] = 4
mapSkip['E,5'] = 5
其他:6
---------------------------------------------------------------
...
主字符串: THIS IS A SIMPLE EXAMPLE (长度:24)
搜索字符串: EXAMPLE (长度:7)
主串中的坏字符的下面字符是:
'X'
mapSkip['E,1'] = 1
其他:2
---------------------------------------------------------------
mapSkip['[任何],0'] = 1
============好后缀数组初始化的流程============================
搜索字符串: SIMPLE EXAMPLE (长度:14)
0 1 2 3 4 5 6 7 8 9 10 11 12 13
S I M P L E E X A M P L E
好后缀的第一个字符为:'E' --> Shift[13] = 6; //以最后一个字符的下标为基准计算要移动的距离;
好后缀的第一个字符为:'L' --> Shift[12] = 8; //"SIMPLE"中有全匹配的, 取全匹配的;
好后缀的第一个字符为:'P' --> Shift[11] = 8;
好后缀的第一个字符为:'M' --> Shift[10] = 8;
好后缀的第一个字符为:'A' --> Shift[9] = 14; //没有全匹配的, 在串头部找子串匹配的, 这里没有, 认为在-1位置(不妨虚拟出来);
...
好后缀的第一个字符为:'I' --> Shift[1] = 14;
好后缀的第一个字符为:'S' --> Shift[0] = 14;//可能需要特殊处理;
E.g. 2
0 1 2 3 4 5 6 7
L E X A M P L E
好后缀的第一个字符为:'E' --> Shift[7] = 6;
好后缀的第一个字符为:'L' --> Shift[6] = 6;
好后缀的第一个字符为:'P' --> Shift[6] = 6;
