Suffix array - YessineJallouli/Competitive-Programming GitHub Wiki

void suffix_array(string &s) {
   s+= '$';
   /// Let's use three vectors :
   /// a contains as left part the pair of two equivalence classes and as the second part the index
   /// p contains the ordering of the strings
   /// c contains the equivalence classes
   int n = s.size();
   vector<int> p(n), c(n);
   {
      vector<pair<char,int>> a(n);
      for (int i = 0; i < n; i++) {
         a[i] = {s[i], i};
      }
      sort(a.begin(), a.end());
      for (int i = 0; i < n; i++)
         p[i] = a[i].second;
      c[p[0]] = 0;
      for (int i = 1; i < n; i++) {
         c[p[i]] = c[p[i-1]];
         if (a[i].first != a[i-1].first)
            c[p[i]]++;
      }
   }
   int k = 0;
   while ((1 << k) < n) {
      vector<pair<pair<int,int>, int>> a(n);
      for (int i = 0; i < n; i++) {
         a[i] = {{c[i], c[(i+(1<<k))%n]}, i};
      }
      sort(a.begin(), a.end());
      for (int i = 0; i < n; i++)
         p[i] = a[i].second;
      c[p[0]] = 0;
      for (int i = 1; i < n; i++) {
         c[p[i]] = c[p[i-1]];
         if (a[i].first != a[i-1].first)
            c[p[i]]++;
      }
      k++;
   }
   for (int i : p)
      cout << i << ' ';
}

void count_sort(vector<int> &p, vector<int> &c) {
   int n = p.size();
   vector<int> cnt(n);
   for (auto x : c) {
      cnt[x]++;
   }
   vector<int> new_p(n);
   vector<int> pos(n);
   pos[0] = 0;
   for (int i = 1; i < n; i++) {
      pos[i] = pos[i-1] + cnt[i-1];
   }
   for (auto x : p) {
      int i = c[x];
      new_p[pos[i]] = x;
      pos[i]++;
   }
   p = new_p;
}
 
void suffix_array(string &s) {
   s+= '$';
   int n = s.size();
   vector<int> p(n), c(n);
   {
      vector<pair<char,int>> a(n);
      for (int i = 0; i < n; i++) {
         a[i] = {s[i], i};
      }
      sort(a.begin(), a.end());
      for (int i = 0; i < n; i++)
         p[i] = a[i].second;
 
      c[p[0]] = 0;
      for (int i = 1; i < n; i++) {
         c[p[i]] = c[p[i-1]];
         if (a[i].first != a[i-1].first)
            c[p[i]]++;
      }
   }
   int k = 0;
   while ((1 << k) < n) {
      for (int i = 0; i < n; i++)
         p[i] = (p[i] - (1 << k) + n) % n;
      count_sort(p,c);
      vector<int> new_c(n);
      new_c[p[0]] = 0;
      for (int i = 1; i < n; i++) {
         new_c[p[i]] = new_c[p[i-1]];
         pair<int,int> p1 = {c[p[i]], c[(p[i]+(1<<k))%n]};
         pair<int,int> p2 = {c[p[i-1]], c[(p[i-1]+(1<<k))%n]};
         if (p1 != p2)
            new_c[p[i]]++;
      }
      c = new_c;
      k++;
   }
   for (int i : p)
      cout << i << ' ';
}