Boyer-Moore算法的C++实现

Boyer-Moore字符串匹配算法是一个在实践当中用得比较多的字符串查找算法，作者实现了一个C++版本的算法，供以后参考。

#include <iostream>#include <algorithm>#include <string>#include <vector>#ifndef ssize_ttypedef off_t ssize_t;#endifusing namespace std;void compute_last_occurrence(const string& needle , vector<ssize_t>& last_occurrence){last_occurrence.resize(256,-1);for ( size_t i = 0 ; i < needle.size() ; i++ ){last_occurrence[needle[i]] = i;}}void compute_prefix_function(const string& needle , vector<size_t>& prefix_function){if ( needle.size() == 0 ){return;}prefix_function.resize( needle.size() , 0 );size_t d = 0 ;for ( size_t i = 1 ; i < needle.size() ; i++ ){while ( d > 0 && needle[d] != needle[i] ){d = prefix_function[d-1];}if ( needle[i] == needle[d] ){d++;}prefix_function[i]=d;}}void compute_goodsuffix_heuristic( const string& needle ,vector<size_t>& goodsuffix_heristic){string reverse_needle;copy( needle.rbegin() , needle.rend() , back_inserter( reverse_needle ) );vector<size_t> prefix_function,reverse_prefix_function;compute_prefix_function( needle , prefix_function );compute_prefix_function( reverse_needle , reverse_prefix_function );size_t m = needle.size();goodsuffix_heristic.resize( m + 1 , m - prefix_function[ m - 1 ] );for ( size_t l = 1 ; l <= m ; l++ ){size_t t = reverse_prefix_function[l-1];size_t j = m - t ;if ( goodsuffix_heristic[j] > l - t ){goodsuffix_heristic[j] = l - t ;}}}void boyer_moore_matcher(const string& haystack,const string& needle){size_t n=haystack.size();size_t m=needle.size();if ( n == 0 || m == 0 || n < m ){cout<<"Invalid input"<<endl;return;}vector<ssize_t> last_occurrence;compute_last_occurrence(needle,last_occurrence);vector<size_t> goodsuffix_heristic;compute_goodsuffix_heuristic( needle , goodsuffix_heristic );size_t offset = 0 ;while ( offset <= n - m ){ssize_t j = m - 1 ;while ( j >= 0 && needle[j] == haystack[offset+j] ){j--;}if ( j < 0 ){cout<<"Find a match at offset "<<offset<<endl;offset += goodsuffix_heristic[0];}else{offset += max<size_t>( goodsuffix_heristic[j+1] ,j - last_occurrence[haystack[offset+j]] );}}}int main(){string haystack,needle;while ( true ){cout<<"Input the haystack:"<<endl;getline(cin,haystack);cout<<"Input the needle:"<<endl;getline(cin,needle);cout<<"Match results:"<<endl;boyer_moore_matcher(haystack,needle);}}