suffix_array.cpp

template <int alphabet = 128>
vector<int> sort_cyclic_shifts(const auto &s) {
  int n = (int)size(s);
  vector<int> p(n), c(n), cnt(max(alphabet, n), 0);
  for (int i = 0; i < n; i++) cnt[s[i]]++;
  for (int i = 1; i < alphabet; i++) cnt[i] += cnt[i - 1];
  for (int i = 0; i < n; i++) p[--cnt[s[i]]] = i;
  c[p[0]] = 0;
  int classes = 1;
  for (int i = 1; i < n; i++) {
    if (s[p[i]] != s[p[i-1]]) classes++;
    c[p[i]] = classes - 1;
  }
  vector<int> pn(n), cn(n);
  for (int h = 0; (1 << h) < n; ++h) {
    for (int i = 0; i < n; i++) {
      pn[i] = p[i] - (1 << h);
      if (pn[i] < 0) pn[i] += n;
    }
    fill(cnt.begin(), cnt.begin() + classes, 0);
    for (int i = 0; i < n; i++) cnt[c[pn[i]]]++;
    for (int i = 1; i < classes; i++) cnt[i] += cnt[i-1];
    for (int i = n-1; ~i; --i) p[--cnt[c[pn[i]]]] = pn[i];
    cn[p[0]] = 0;
    classes = 1;
    for (int i = 1; i < n; i++) {
      pair<int, int> cur = {c[p[i]], c[(p[i]+(1<<h))%n]};
      pair<int, int> prev = {c[p[i-1]], c[(p[i-1]+(1<<h))%n]};
      if (cur != prev) ++classes;
      cn[p[i]] = classes-1;
    }
    c.swap(cn);
  }
  return p;
}
template <int sz = 256>
vector<int> suffix_array(auto s) {
  s.push_back(0);
  auto res = sort_cyclic_shifts<sz>(s);
  res.erase(begin(res));
  return res;
}