Luzhiled's Library

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:heavy_check_mark: Rolling-Hash(ローリングハッシュ)
(string/rolling-hash.cpp)

概要

文字列の一致判定を mod $2^{61}-1$ のハッシュを用いて効率的に行う.

計算量

Verified with

Code

/**
 * @brief Rolling-Hash(ローリングハッシュ)
 * @see https://qiita.com/keymoon/items/11fac5627672a6d6a9f6
 * @docs docs/rolling-hash.md
 */
struct RollingHash {
  static const uint64_t mod = (1ull << 61ull) - 1;
  using uint128_t = __uint128_t;
  vector< uint64_t > power;
  const uint64_t base;

  static inline uint64_t add(uint64_t a, uint64_t b) {
    if((a += b) >= mod) a -= mod;
    return a;
  }

  static inline uint64_t mul(uint64_t a, uint64_t b) {
    uint128_t c = (uint128_t) a * b;
    return add(c >> 61, c & mod);
  }

  static inline uint64_t generate_base() {
    mt19937_64 mt(chrono::steady_clock::now().time_since_epoch().count());
    uniform_int_distribution< uint64_t > rand(1, RollingHash::mod - 1);
    return rand(mt);
  }

  inline void expand(size_t sz) {
    if(power.size() < sz + 1) {
      int pre_sz = (int) power.size();
      power.resize(sz + 1);
      for(int i = pre_sz - 1; i < sz; i++) {
        power[i + 1] = mul(power[i], base);
      }
    }
  }

  explicit RollingHash(uint64_t base = generate_base()) : base(base), power{1} {}

  vector< uint64_t > build(const string &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for(int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  template< typename T >
  vector< uint64_t > build(const vector< T > &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for(int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  uint64_t query(const vector< uint64_t > &s, int l, int r) {
    expand(r - l);
    return add(s[r], mod - mul(s[l], power[r - l]));
  }

  uint64_t combine(uint64_t h1, uint64_t h2, size_t h2len) {
    expand(h2len);
    return add(mul(h1, power[h2len]), h2);
  }

  int lcp(const vector< uint64_t > &a, int l1, int r1, const vector< uint64_t > &b, int l2, int r2) {
    int len = min(r1 - l1, r2 - l2);
    int low = 0, high = len + 1;
    while(high - low > 1) {
      int mid = (low + high) / 2;
      if(query(a, l1, l1 + mid) == query(b, l2, l2 + mid)) low = mid;
      else high = mid;
    }
    return low;
  }
};
#line 1 "string/rolling-hash.cpp"
/**
 * @brief Rolling-Hash(ローリングハッシュ)
 * @see https://qiita.com/keymoon/items/11fac5627672a6d6a9f6
 * @docs docs/rolling-hash.md
 */
struct RollingHash {
  static const uint64_t mod = (1ull << 61ull) - 1;
  using uint128_t = __uint128_t;
  vector< uint64_t > power;
  const uint64_t base;

  static inline uint64_t add(uint64_t a, uint64_t b) {
    if((a += b) >= mod) a -= mod;
    return a;
  }

  static inline uint64_t mul(uint64_t a, uint64_t b) {
    uint128_t c = (uint128_t) a * b;
    return add(c >> 61, c & mod);
  }

  static inline uint64_t generate_base() {
    mt19937_64 mt(chrono::steady_clock::now().time_since_epoch().count());
    uniform_int_distribution< uint64_t > rand(1, RollingHash::mod - 1);
    return rand(mt);
  }

  inline void expand(size_t sz) {
    if(power.size() < sz + 1) {
      int pre_sz = (int) power.size();
      power.resize(sz + 1);
      for(int i = pre_sz - 1; i < sz; i++) {
        power[i + 1] = mul(power[i], base);
      }
    }
  }

  explicit RollingHash(uint64_t base = generate_base()) : base(base), power{1} {}

  vector< uint64_t > build(const string &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for(int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  template< typename T >
  vector< uint64_t > build(const vector< T > &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for(int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  uint64_t query(const vector< uint64_t > &s, int l, int r) {
    expand(r - l);
    return add(s[r], mod - mul(s[l], power[r - l]));
  }

  uint64_t combine(uint64_t h1, uint64_t h2, size_t h2len) {
    expand(h2len);
    return add(mul(h1, power[h2len]), h2);
  }

  int lcp(const vector< uint64_t > &a, int l1, int r1, const vector< uint64_t > &b, int l2, int r2) {
    int len = min(r1 - l1, r2 - l2);
    int low = 0, high = len + 1;
    while(high - low > 1) {
      int mid = (low + high) / 2;
      if(query(a, l1, l1 + mid) == query(b, l2, l2 + mid)) low = mid;
      else high = mid;
    }
    return low;
  }
};
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