Submission #1097745

#	Time	Username	Problem	Language	Result	Execution time	Memory
1097745		duckindog	Palindromes (APIO14_palindrome)	C++17	23 / 100	1055 ms	12936 KiB

palindrome

#include <bits/stdc++.h>

using namespace std;

const int N = 300'000 + 10;
string s;
int n;

struct Hash { 
  int base, M;
  vector<int> h, rh, pw;
  Hash() : base(0), M(0) {}
  Hash(string s, int base, int M) : base(base), M(M), h(s.size() + 1), rh(s.size() + 1), pw(s.size() + 1) { 
    pw[0] = 1;
    for (int i = 1; i <= n; ++i) { 
      pw[i] = 1ll * pw[i - 1] * base % M;
      h[i] = (1ll * h[i - 1] * base % M + s[i - 1]) % M;
      rh[i] = (1ll * rh[i - 1] * base % M + s[n - i]) % M;
    }
  }

  int get(int l, int r) { 
    return (h[r] - 1ll * h[l - 1] * pw[r - l + 1] % M + M) % M; 
  }
  int rget(int l, int r) { 
    return (rh[r] - 1ll * rh[l - 1] * pw[r - l + 1] % M + M) % M; 
  }
} T[2];

using HASH = pair<int, int>;
inline HASH get(int l, int r) { 
  return make_pair(T[0].get(l, r), T[1].get(l, r));
}
inline HASH rget(int l, int r) { 
  tie(l, r) = make_pair(n - r + 1, n - l + 1);
  return make_pair(T[0].rget(l, r), T[1].rget(l, r));
}
inline bool chk(int l, int r) { return get(l, r) == rget(l, r); }

int pos[N], tmp[N], sa[N];
int lcp[N];

void initSA() { 
  for (int i = 1; i <= n; ++i) pos[i] = s[i] - 'a' + 1, sa[i] = i;
  for (int gap = 1; ; gap *= 2) { 
    auto cmp = [&](int i, int j) { 
      if (pos[i] != pos[j]) return pos[i] < pos[j];
      i += gap; j += gap;
      return i <= n && j <= n ? pos[i] < pos[j] : i > j;
    };
    
    sort(sa + 1, sa + n + 1, cmp);
    for (int i = 2; i <= n; ++i) tmp[i] = tmp[i - 1] + cmp(sa[i - 1], sa[i]);
    for (int i = 1; i <= n; ++i) pos[sa[i]] = tmp[i] + 1;
    if (tmp[n] == n - 1) break;
  }
  
  for (int i = 1, k = 0; i <= n; ++i) { 
    if (pos[i] == n) continue;
    for (int j = sa[pos[i] + 1]; s[i + k] == s[j + k]; ) k += 1;
    lcp[i] = k;
    if (k) k -= 1;
  }
}

long long value[N];

int32_t main() { 
  cin.tie(0)->sync_with_stdio(0);

  cin >> s;
  n = s.size();
  
  T[0] = Hash(s, 19937, 1e9 + 7);
  T[1] = Hash(s, 10007, 1e9 + 9);
  
  s = '@' + s;
  initSA();
  long long answer = 0;
  for (int i = 1; i <= n; ++i) { 
    for (int j = lcp[sa[i - 1]]; j > lcp[sa[i]]; --j)
      if (chk(sa[i - 1], sa[i - 1] + j - 1)) value[j] = 0;
    
    for (int j = 1; j <= lcp[sa[i]]; ++j)
      if (chk(sa[i], sa[i] + j - 1)) value[j] += j;
    
    for (int j = 1; j <= n - sa[i] + 1; ++j) 
      if (chk(sa[i], sa[i] + j - 1)) answer = max(answer, value[j] + j);
  }

  cout << answer << "\n";
}

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 0 / 24
• Subtask 4: 0 / 26
• Subtask 5: 0 / 27