Submission #582973

#	Time	Username	Problem	Language	Result	Execution time	Memory
582973		600Mihnea	Palindromic Partitions (CEOI17_palindromic)	C++17	15 / 100	17 ms	8204 KiB

palindromic

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int M = (int) 1e9 + 7;

int add(int a, int b) {
  a += b;
  if (a >= M) return a - M;
  if (a < 0) return a + M;
  return a;
}

int mul(int a, int b) {
  return a * (ll) b % M;
}

int pw(int a, int b) {
  int r = 1;
  while (b) {
    if (b & 1) {
      r = mul(r, a);
    }
    a = mul(a, a);
    b /= 2;
  }
  return r;
}

int dv(int a, int b) {
  return mul(a, pw(b, M - 2));
}

void addup(int &a, int b) {
  a = add(a, b);
}

void mulup(int &a, int b) {
  a = mul(a, b);
}

const int N = (int) 1e6 + 7;
const int INF = (int) 1e9 + 7;
const int BASS = 37;
int n;
int a[N];
int dp[N];
int big[N];
int s[2][N], p[N], ip[N];

bool is_palind(int l, int r) {
  if (l > r) {
    return 1;
  }
  return a[l] == a[r] && is_palind(l + 1, r - 1);
}

int get(int type, int l, int r) {
  int sol = add(s[type][r], -s[type][l - 1]);
  return mul(sol, ip[l - 1]);
}

bool pali(int l, int r) {
  return get(0, l, r) == get(1, n + 1 - r, n + 1 - l);
}

signed main() {
  ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

  {
    p[0] = 1;
    for (int i = 1; i < N; i++) {
      p[i] = mul(p[i - 1], BASS);
    }

    ip[N - 1] = dv(1, p[N - 1]);
    for (int i = N - 2; i >= 0; i--) {
      ip[i] = mul(ip[i + 1], BASS);
    }

  }

///  freopen ("input.txt", "r", stdin);

  int Tests;
  cin >> Tests;
  for (int tc = 1; tc <= Tests; tc++) {
    {
      string str;
      cin >> str;
      n = (int) str.size();
      int Low = 0, High = n - 1;
      for (int Step = 1; Step <= n; Step++) {
        if (Step % 2 == 0) {
          a[Step] = str[Low++] - 'a';
        } else {
          a[Step] = str[High--] - 'a';
        }
      }
    }

    for (int i = 1; i <= n; i++) {
      s[0][i] = add(s[0][i - 1], mul(p[i], a[i]));
      s[1][i] = add(s[1][i - 1], mul(p[i], a[n + 1 - i]));
    }

    for (int i = 0; i <= n + 1; i++) {
      dp[i] = -INF;
      big[i] = 0;
    }
    set<int> R;
    for (int i = 1; i <= n; i++) {
      R.insert(i);
    }
    dp[0] = 0;
    for (int i = n - 1; i >= 1; i--) {
      while (1) {
        int r;
        {
          auto it = R.lower_bound(i + 1);
          if (it == R.end()) {
            break;
          }
          r = *it;
        }
        int l = 2 * i + 1 - r;
        if (is_palind(l, r)) {
          R.erase(r);
          big[r] = i;
        } else {
          break;
        }
      }
    }

    for (int r = 1; r <= n; r++) {
      if (int i = big[r]) {
        int l = 2 * i + 1 - r;
        dp[r] = max(dp[r], dp[l - 1] + 1);
      }
    }
    int sol = 2 * dp[n];
    for (int i = 0; i < n; i++) {
      sol = max(sol, 2 * dp[i] + 1);
    }
    cout << sol << "\n";
  }
}

• Subtask 1: 15 / 15
• Subtask 2: 0 / 20
• Subtask 3: 0 / 25
• Subtask 4: 0 / 40