SuffixArray

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SuffixArray sufa(s);

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auto res = sufa.lower_upper_bound(t);

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struct SuffixArray {
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  vector<int> SA;
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  const string s;
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  SuffixArray(const string &str) : s(str) {
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    SA.resize(s.size());
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    iota(begin(SA), end(SA), 0);
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    sort(begin(SA), end(SA), [&](int a, int b) {
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      return s[a] == s[b] ? a > b : s[a] < s[b];
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    });
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    vector<int> classes(s.size()), c(s.begin(), s.end()), cnt(s.size());
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    for (int len = 1; len < s.size(); len <<= 1) {
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      for (int i = 0; i < s.size(); i++) {
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        if (i > 0 && c[SA[i - 1]] == c[SA[i]] && SA[i - 1] + len < s.size() && c[SA[i - 1] + len / 2] == c[SA[i] + len / 2]) {
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          classes[SA[i]] = classes[SA[i - 1]];
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        } else {
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          classes[SA[i]] = i;
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        }
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      }
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      iota(begin(cnt), end(cnt), 0);
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      copy(begin(SA), end(SA), begin(c));
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      for (int i = 0; i < s.size(); i++) {
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        int s1 = c[i] - len;
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        if (s1 >= 0)
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          SA[cnt[classes[s1]]++] = s1;
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      }
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      classes.swap(c);
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    }
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  }
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  int operator[](int k) const {
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    return SA[k];
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  }
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  size_t size() const {
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    return s.size();
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  }
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  bool lt_substr(const string &t, int si = 0, int ti = 0) {
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    int sn = (int)s.size(), tn = (int)t.size();
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    while (si < sn && ti < tn) {
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      if (s[si] < t[ti])
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        return true;
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      if (s[si] > t[ti])
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        return false;
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      ++si, ++ti;
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    }
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    return si >= sn && ti < tn;
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  }
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  int lower_bound(const string &t) {
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    int low = -1, high = (int)SA.size();
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    while (high - low > 1) {
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      int mid = (low + high) / 2;
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      if (lt_substr(t, SA[mid]))
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        low = mid;
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      else
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        high = mid;
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    }
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    return high;
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  }
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  pair<int, int> lower_upper_bound(string &t) {
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    int idx = lower_bound(t);
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    int low = idx - 1, high = (int)SA.size();
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    t.back()++;
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    while (high - low > 1) {
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      int mid = (low + high) / 2;
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      if (lt_substr(t, SA[mid]))
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        low = mid;
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      else
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        high = mid;
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    }
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    t.back()--;
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    return {idx, high};
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  }
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  void output() {
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    for (int i = 0; i < size(); i++) {
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      cout << i << ": " << s.substr(SA[i]) << endl;
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    }
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  }
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};