Submission #891638

#	Time	Username	Problem	Language	Result	Execution time	Memory
891638		tch1cherin	Palindromes (APIO14_palindrome)	C++17	100 / 100	437 ms	57388 KiB

palindrome

#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
using namespace std;

vector<int> suffix_array(string S) {
  S += "$";
  int N = (int)S.size();
  vector<int> ord(N), comp(N);
  for (int i = 0; i < N; i++) {
    ord[i] = i;
    comp[i] = S[i];
  }
  sort(ord.begin(), ord.end(), [&](int i, int j) { return S[i] < S[j]; });
  vector<int> tmp(N), cnt(N + 1);
  auto Update = [&](int d) {
    int ptr = 0, x = -1, y = -1;
    for (int i : ord) {
      int j = i + d < N ? i + d : i + d - N;
      tmp[i] = comp[i] != x || comp[j] != y ? ++ptr : ptr;
      x = comp[i], y = comp[j];
    }
    comp = tmp;
  };
  auto Sort = [&](int d) {
    cnt.assign(N + 1, 0);
    for (int value : comp) {
      cnt[value]++;
    }
    partial_sum(cnt.begin(), cnt.end(), cnt.begin());
    for (int i : ord) {
      int j = i + d < N ? i + d : i + d - N;
      tmp[cnt[comp[j] - 1]++] = i;
    }
    ord = tmp;
  };
  Update(0);
  for (int d = 1; d < N; d += d) {
    Sort(d);
    Sort(0);
    Update(d);
  }
  return ord;
}

vector<int> find_lcp(string S, vector<int> ord) {
  S += "$";
  int N = (int)S.size();
  vector<int> pos(N);
  for (int i = 0; i < N; i++) {
    pos[ord[i]] = i;
  }
  vector<int> lcp(N);
  int l = 0;
  for (int i = 0; i < N; i++) {
    if (pos[i] == N - 1) {
      continue;
    }
    int j = ord[pos[i] + 1];
    while (max(i, j) + l < N && S[i + l] == S[j + l]) {
      l++;
    }
    lcp[pos[i]] = l;
    l = max(0, l - 1);
  }
  return lcp;
}

vector<int> manacher_odd(string S) {
  S += "$";
  int N = (int)S.size();
  vector<int> x(N, 1);
  int l = 0, r = 0;
  for (int i = 1; i < N; i++) {
    if (i < r) {
      x[i] = min(r - i + 1, x[l + r - i]);
    }
    while (i - x[i] >= 0 && i + x[i] < N && S[i - x[i]] == S[i + x[i]]) {
      x[i]++;
    }
    if (i + x[i] - 1 > r) {
      l = i - x[i] + 1;
      r = i + x[i] - 1;
    }
  }
  x.pop_back();
  return x;
}

vector<int> manacher_even(string s) {
  int n = (int)s.size();
  vector<int> d(n, 0);
  int l = -1, r = -1;
  for (int i = 0; i < n - 1; i++) {
    if (i < r) {
      d[i] = min(r - i, d[l + r - i - 1]);
    }
    while (i - d[i] >= 0 && i + d[i] + 1 < n && s[i - d[i]] == s[i + d[i] + 1]) {
      d[i]++;
    }
    if (i + d[i] > r) {
      l = i - d[i] + 1, r = i + d[i];
    }
  }
  rotate(d.rbegin(), d.rbegin() + 1, d.rend());
  return d;
}

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  string S;
  cin >> S;
  int N = (int)S.size();
  vector<int> ord = suffix_array(S);
  vector<int> lcp = find_lcp(S, ord);
  vector<int> x_odd = manacher_odd(S), x_even = manacher_even(S);
  vector<int> pos(N + 1);
  for (int i = 0; i <= N; i++) {
    pos[ord[i]] = i;
  }
  vector<int> max_pal(N + 1);
  set<int> odd, even;
  vector<vector<int>> del_odd(N), del_even(N);
  for (int i = N - 1; i >= 0; i--) {
    odd.insert(i);
    even.insert(i);
    del_odd[i - x_odd[i] + 1].push_back(i);
    del_even[i - x_even[i]].push_back(i);
    max_pal[pos[i]] = max((*odd.rbegin() - i) * 2 + 1, (*even.rbegin() - i) * 2);
    for (int v : del_odd[i]) {
      odd.erase(v);
    }
    for (int v : del_even[i]) {
      even.erase(v);
    }
  }
  vector<int> A;
  for (int i = 0; i <= N; i++) {
    A.push_back(max_pal[i]);
    A.push_back(lcp[i]);
  }
  long long ans = 1;
  vector<int> L(2 * (N + 1)), R(2 * (N + 1));
  stack<int> st;
  for (int i = 0; i < 2 * (N + 1); i++) {
    while (!st.empty() && A[i] <= A[st.top()]) {
      st.pop();
    }
    L[i] = st.empty() ? -1 : st.top();
    st.push(i);
  }
  st = stack<int>();
  for (int i = 2 * (N + 1) - 1; i >= 0; i--) {
    while (!st.empty() && A[i] <= A[st.top()]) {
      st.pop();
    }
    R[i] = st.empty() ? 2 * (N + 1) : st.top();
    if (i % 2 == 0) {
      ans = max(ans, 1LL * ((R[i] - L[i] + 1) / 2) * A[i]);
    }
    st.push(i);
  } 
  cout << ans << "\n";
}

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 24 / 24
• Subtask 4: 26 / 26
• Subtask 5: 27 / 27