Boyer-Moore算法的C++实现

最新推荐文章于 2024-02-28 07:31:58 发布

oyster2008

最新推荐文章于 2024-02-28 07:31:58 发布

阅读量1.8k

点赞数

分类专栏： C/C++ 文章标签：算法 c++ function string c

本文链接：https://blog.youkuaiyun.com/oyster2008/article/details/5673752

版权

C/C++ 专栏收录该内容

4 篇文章

订阅专栏

本文介绍了一种高效的字符串搜索算法——Boyer-Moore算法，并提供了详细的C++实现代码。该算法通过预处理模式串计算偏移表，利用字符跳过和好后缀原则快速定位目标子串。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

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_t typedef off_t ssize_t; #endif using 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); } }