String_Search.H

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
 
# ifndef STRING_SEARCH_H
# define STRING_SEARCH_H
 
# include <cstdint>
# include <algorithm>
# include <string>
# include <string_view>
# include <array>
 
# include <tpl_array.H>
 
namespace Aleph
{
  namespace string_search_detail
  {
    inline Array<size_t> all_match_positions(const size_t text_size)
    {
      Array<size_t> matches;
      matches.reserve(text_size + 1);
      for (size_t i = 0; i <= text_size; ++i)
        matches.append(i);
      return matches;
    }
 
 
    inline bool find_unused_delimiter(const std::string_view a,
                                      const std::string_view b,
                                      char & delimiter)
    {
      std::array<bool, 256> used{};
      used.fill(false);
      for (const unsigned char c : a)
        used[c] = true;
 
      for (const unsigned char c : b)
        used[c] = true;
 
      for (size_t i = 0; i < 256; ++i)
        if (not used[i])
          {
            delimiter = static_cast<char>(i);
            return true;
          }
 
      return false;
    }
 
 
    inline bool equals_at(const std::string_view text,
                          const std::string_view pattern,
                          const size_t pos)
    {
      for (size_t i = 0; i < pattern.size(); ++i)
        if (text[pos + i] != pattern[i])
          return false;
      return true;
    }
  } // namespace string_search_detail
 
 
  inline Array<size_t> kmp_prefix_function(const std::string_view pattern)
  {
    Array<size_t> pi;
    if (pattern.empty())
      return pi;
 
    pi = Array<size_t>::create(pattern.size());
    pi[0] = 0;
 
    size_t j = 0;
    for (size_t i = 1; i < pattern.size(); ++i)
      {
        while (j > 0 and pattern[i] != pattern[j])
          j = pi[j - 1];
 
        if (pattern[i] == pattern[j])
          ++j;
 
        pi[i] = j;
      }
 
    return pi;
  }
 
 
  inline Array<size_t> kmp_search(const std::string_view text,
                                  const std::string_view pattern)
  {
    if (pattern.empty())
      return string_search_detail::all_match_positions(text.size());
 
    Array<size_t> matches;
    if (text.size() < pattern.size())
      return matches;
 
    const Array<size_t> pi = kmp_prefix_function(pattern);
 
    size_t j = 0;
    for (size_t i = 0; i < text.size(); ++i)
      {
        while (j > 0 and text[i] != pattern[j])
          j = pi[j - 1];
 
        if (text[i] == pattern[j])
          ++j;
 
        if (j == pattern.size())
          {
            matches.append(i + 1 - pattern.size());
            j = pi[j - 1];
          }
      }
 
    return matches;
  }
 
 
  inline Array<size_t> z_algorithm(const std::string_view s)
  {
    Array<size_t> z;
    if (s.empty())
      return z;
 
    z = Array<size_t>::create(s.size());
    z[0] = s.size();
 
    size_t l = 0;
    size_t r = 0;
 
    for (size_t i = 1; i < s.size(); ++i)
      {
        if (i <= r)
          z[i] = std::min(r - i + 1, z[i - l]);
        else
          z[i] = 0;
 
        while (i + z[i] < s.size() and s[z[i]] == s[i + z[i]])
          ++z[i];
 
        if (const size_t reach = i + z[i]; reach > r + 1)
          {
            l = i;
            r = reach - 1;
          }
      }
 
    return z;
  }
 
 
  inline Array<size_t> z_search(const std::string_view text,
                                const std::string_view pattern)
  {
    if (pattern.empty())
      return string_search_detail::all_match_positions(text.size());
 
    if (text.size() < pattern.size())
      return {};
 
    char delimiter = 0;
    if (not string_search_detail::find_unused_delimiter(pattern, text, delimiter))
      return kmp_search(text, pattern);
 
    std::string combined;
    combined.reserve(pattern.size() + text.size() + 1);
    combined += pattern;
    combined += delimiter;
    combined += text;
 
    const Array<size_t> z = z_algorithm(combined);
 
    Array<size_t> matches;
    const size_t offset = pattern.size() + 1;
    for (size_t i = offset; i < combined.size(); ++i)
      if (z[i] >= pattern.size())
        matches.append(i - offset);
 
    return matches;
  }
 
 
  inline Array<size_t> boyer_moore_horspool_search(const std::string_view text,
                                                   const std::string_view pattern)
  {
    if (pattern.empty())
      return string_search_detail::all_match_positions(text.size());
 
    Array<size_t> matches;
    const size_t n = text.size();
    const size_t m = pattern.size();
 
    if (n < m)
      return matches;
 
    Array<size_t> shift = Array<size_t>::create(256);
    for (size_t i = 0; i < 256; ++i)
      shift[i] = m;
 
    for (size_t i = 0; i + 1 < m; ++i)
      shift[static_cast<unsigned char>(pattern[i])] = m - 1 - i;
 
    size_t i = 0;
    while (i + m <= n)
      {
        size_t j = m;
        while (j > 0 and pattern[j - 1] == text[i + j - 1])
          --j;
 
        if (j == 0)
          matches.append(i);
 
        const auto c = static_cast<unsigned char>(text[i + m - 1]);
        const size_t step = shift[c] == 0 ? 1 : shift[c];
        i += step;
      }
 
    return matches;
  }
 
 
  inline Array<size_t> rabin_karp_search(const std::string_view text,
                                         const std::string_view pattern,
                                         const uint64_t base = 911382323ull)
  {
    if (pattern.empty())
      return string_search_detail::all_match_positions(text.size());
 
    Array<size_t> matches;
    const size_t n = text.size();
    const size_t m = pattern.size();
 
    if (n < m)
      return matches;
 
    uint64_t power = 1;
    for (size_t i = 1; i < m; ++i)
      power *= base;
 
    uint64_t pattern_hash = 0;
    uint64_t window_hash = 0;
 
    for (size_t i = 0; i < m; ++i)
      {
        pattern_hash = pattern_hash * base
                       + static_cast<unsigned char>(pattern[i]) + 1ull;
        window_hash = window_hash * base
                      + static_cast<unsigned char>(text[i]) + 1ull;
      }
 
    if (window_hash == pattern_hash
        and string_search_detail::equals_at(text, pattern, 0))
      matches.append(0);
 
    for (size_t i = m; i < n; ++i)
      {
        const uint64_t old_c = static_cast<unsigned char>(text[i - m]) + 1ull;
        const uint64_t new_c = static_cast<unsigned char>(text[i]) + 1ull;
 
        window_hash = (window_hash - old_c * power) * base + new_c;
 
        if (const size_t pos = i + 1 - m; window_hash == pattern_hash
                                          and string_search_detail::equals_at(text, pattern, pos))
          matches.append(pos);
      }
 
    return matches;
  }
} // namespace Aleph
 
# endif // STRING_SEARCH_H