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rabin_karp.cpp
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70 lines (59 loc) · 1.78 KB
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#include "rabin_karp.h"
auto RabinKarp::RabinKarpMatcher1(const std::string& text, const std::string& pattern) -> std::vector<int>
{
std::vector<int> result;
if (text.size() < pattern.size())
{
return result;
}
const size_t pattern_hash = std::hash<std::string>{}(pattern);
for (int i = 0; i <= static_cast<int>(text.size()) - static_cast<int>(pattern.size()); ++i)
{
const size_t next_hash = std::hash<std::string>{}(text.substr(i, pattern.size()));
if (next_hash == pattern_hash && text.substr(i, pattern.size()) == pattern)
{
result.emplace_back(i);
}
}
return result;
}
auto RabinKarp::RabinKarpMatcher2(const std::string& text, const std::string& pattern) -> std::vector<int>
{
std::vector<int> result;
if (text.size() < pattern.size())
{
return result;
}
constexpr int base = 256;
constexpr int prime = 101;
int pattern_hash = 0;
for (const char ch : pattern)
{
pattern_hash = (base * pattern_hash + ch) % prime;
}
for (int i = 0; i <= static_cast<int>(text.size()) - static_cast<int>(pattern.size()); ++i)
{
int next_hash = 0;
for (int j = 0; j < static_cast<int>(pattern.size()); ++j)
{
next_hash = (base * next_hash + text[i + j]) % prime;
}
if (pattern_hash == next_hash)
{
bool is_match = true;
for (int j = 0; j < static_cast<int>(pattern.size()); ++j)
{
if (text[i + j] != pattern[j])
{
is_match = false;
break;
}
}
if (is_match)
{
result.emplace_back(i);
}
}
}
return result;
}