Submission #617101

#	Time	Username	Problem	Language	Result	Execution time	Memory
617101		juancarlovieri	Palinilap (COI16_palinilap)	C++17	100 / 100	89 ms	24888 KiB

palinilap

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define mod 1000000007

mt19937 gen(33);
uniform_int_distribution<> rd(1, 1000000000);
int pre[100005];
int prer[100005];
int pw[100005];
int p;
int all[100005][26];
int n;

int take(int l, int r) {
  int res = pre[r];
  if (l) {
    res -= pw[r - l + 1] * pre[l - 1] % mod;
  }
  res += mod;
  res %= mod;
  return res;
}

int takerev(int l, int r) {
  int res = prer[r];
  if (r) {
    res -= pw[r - l + 1] * prer[l - 1] % mod;
  }
  res += mod;
  res %= mod;
  return res;
}

bool eq(int a, int b, int c, int d) {
  return take(a, b) == takerev(n - d - 1, n - c - 1);
}

signed main() {
  p = rd(gen);
  string s;
  cin >> s;
  n = s.length();
  auto srev = s;
  reverse(srev.begin(), srev.end());
  pw[0] = 1;
  for (int i = 1; i < n; ++i) pw[i] = pw[i - 1] * p % mod;
  pre[0] = s[0] % mod;
  for (int i = 1; i < n; ++i) {
    pre[i] = (pre[i - 1] * p % mod + s[i]) % mod;
  }
  prer[0] = srev[0] % mod;
  for (int i = 1; i < n; ++i) {
    prer[i] = (prer[i - 1] * p % mod + srev[i]) % mod;
  }
  int act = 0;
  vector<pair<int, int>> diff(n + 5);
  // cout << pw[2] << endl;
  // cout << take(0, 1) <<  ' ' << take(2, 3) << endl;

  for (int i = 0; i < n; ++i) {
    for (int j = i; j <= i + 1; ++j) {
      if (j >= n) continue;
      int lo = 0, hi = min(i, n - j - 1);
      while (lo <= hi) {
        int mid = (lo + hi) / 2;
        if (eq(i - mid, i, j, j + mid)) {
        // if (take(i - mid, i) == take(j, j + mid)) {
          lo = mid + 1;
        } else hi = mid - 1;
      }
      if (hi >= 0) {
        // assert(take(i - hi, i) == take(j, j + hi)); 
      }
      // cout << "hi" << hi << ' ' << take(0, 1) << ' ' << takerev(0, 1) << endl;
      act += hi + 1;
      if (i == j) {
        diff[j + 1].first += -1;
        diff[j + hi + 1].first -= - 1;
        diff[j + 1].second += j + hi + 1;
        diff[j + hi + 1].second -= j + hi + 1;

        diff[i - (hi + 1) + 1].first += 1;
        diff[i].first -= 1;
        diff[i - (hi + 1) + 1].second += -(i - (hi + 1));
        diff[i].second -= -(i - (hi + 1));
      } else {
        diff[j].first += -1;
        diff[j + hi + 1].first -= - 1;
        diff[j].second += j + hi + 1;
        diff[j + hi + 1].second -= j + hi + 1;

        diff[i - (hi + 1) + 1].first += 1;
        diff[i + 1].first -= 1;
        diff[i - (hi + 1) + 1].second += -(i - (hi + 1));
        diff[i + 1].second -= -(i - (hi + 1));
      }

      int x = i - hi - 1;
      int y = j + hi + 1;
      if (x < 0 or y > n - 1) continue;
      lo = 1, hi = min(x, n - y - 1);
      while (lo <= hi) {
        int mid = (lo + hi) / 2;
        if (eq(x - mid, x - 1, y + 1, y + mid)) {
        // if (take(x - mid, x - 1) == take(y + 1, y + mid)) {
          lo = mid + 1;
        } else hi = mid - 1;
      }
      if (hi > 0) {
        // assert(take(x - hi, x - 1) == take(y + 1, y + hi));
      }
      // if (i == 0 and j == 1) cout << x << ' ' << y << ' ' << hi + 1 << endl;
      all[x][s[y] - 'a'] += hi + 1;
      all[y][s[x] - 'a'] += hi + 1;
    }
  }
  int ans = act;
  int cur = act;
  // cout << cur << endl;
  int delta = 0;
  int m = 0, c=  0;
  for (int i = 0; i < n; ++i) {
    // delta += diff[i];
    // cur += delta;
    m += diff[i].first;
    c += diff[i].second;
    // cout << delta << endl; 
    for (int j = 0; j < 26; ++j) {
      if ((s[i] - 'a') == j) continue;
      // cout << all[i][j] << ' ';
      // if (i == 1 and j == 2) cout << "INI " << all[i][j] << endl;
      ans = max(ans, cur + all[i][j] - (i * m + c));
      // if (i == 1 and j == 0) cout << cur << endl;
      // cout << i << ' ' << j << ' ' << cur + all[i][j] + 1 << endl;
    }
    // cout << endl;
    // cout << cur << ' ';
  }
  // cout << endl;
  cout << ans << endl;
  // delta += diff[n];
  // cur += delta;
  assert(cur == act);
  // cout << cur << endl;
}

Compilation message (stderr)

palinilap.cpp: In function 'int main()':
palinilap.cpp:122:7: warning: unused variable 'delta' [-Wunused-variable]
  122 |   int delta = 0;
      |       ^~~~~

• Subtask 1: 17 / 17
• Subtask 2: 37 / 37
• Subtask 3: 46 / 46