algorithm-examples/cpp-algorithm/src/string/rabin_karp.cpp at main · codejsha/algorithm-examples · GitHub

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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;

}

algorithm-examples/cpp-algorithm/src/string/rabin_karp.cpp at main · codejsha/algorithm-examples · GitHub

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