Manacher(最長回文) (string/manacher.hpp)

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• Last update: 2024-04-27 01:27:28+09:00
• Include: #include "string/manacher.hpp"

Verified with

• test/verify/yosupo-enumerate-palindromes.test.cpp

Code

/**
 * @brief Manacher(最長回文)
 */
template <typename S>
vector<int> manacher(S s, bool calc_even = true) {
  if (calc_even) {
    int n = (int)s.size();
    assert(n > 0);
    s.resize(2 * n - 1);
    for (int i = n - 1; i >= 0; i--) {
      s[2 * i] = s[i];
    }
    auto d = *min_element(begin(s), end(s));
    for (int i = 0; i < n - 1; i++) {
      s[2 * i + 1] = d;
    }
  }
  int n = (int)s.size();
  vector<int> rad(n);
  {
    int i = 0, j = 0;
    while (i < n) {
      while (i - j >= 0 && i + j < n && s[i - j] == s[i + j]) ++j;
      rad[i] = j;
      int k = 1;
      while (i - k >= 0 && i + k < n && k + rad[i - k] < j) {
        rad[i + k] = rad[i - k];
        ++k;
      }
      i += k, j -= k;
    }
  }
  if (calc_even) {
    for (int i = 0; i < n; i++) {
      if (((i ^ rad[i]) & 1) == 0) rad[i]--;
    }
  } else {
    for (auto &&x : rad) x = 2 * x - 1;
  }
  return rad;
}

#line 1 "string/manacher.hpp"
/**
 * @brief Manacher(最長回文)
 */
template <typename S>
vector<int> manacher(S s, bool calc_even = true) {
  if (calc_even) {
    int n = (int)s.size();
    assert(n > 0);
    s.resize(2 * n - 1);
    for (int i = n - 1; i >= 0; i--) {
      s[2 * i] = s[i];
    }
    auto d = *min_element(begin(s), end(s));
    for (int i = 0; i < n - 1; i++) {
      s[2 * i + 1] = d;
    }
  }
  int n = (int)s.size();
  vector<int> rad(n);
  {
    int i = 0, j = 0;
    while (i < n) {
      while (i - j >= 0 && i + j < n && s[i - j] == s[i + j]) ++j;
      rad[i] = j;
      int k = 1;
      while (i - k >= 0 && i + k < n && k + rad[i - k] < j) {
        rad[i + k] = rad[i - k];
        ++k;
      }
      i += k, j -= k;
    }
  }
  if (calc_even) {
    for (int i = 0; i < n; i++) {
      if (((i ^ rad[i]) & 1) == 0) rad[i]--;
    }
  } else {
    for (auto &&x : rad) x = 2 * x - 1;
  }
  return rad;
}

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