Submission #1106228

#	Time	Username	Problem	Language	Result	Execution time	Memory
1106228		ducanh1234	Palindromes (APIO14_palindrome)	C++17	100 / 100	680 ms	36268 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;
  }
}
 
int f[N][19], lg[N];
void init() { 
  for (int i = 2; i <= n; ++i) lg[i] = lg[i >> 1] + 1;
  for (int i = 1; i <= n; ++i) f[i][0] = lcp[sa[i]];
  for (int j = 1; j <= 18; ++j) { 
    for (int i = 1; i <= n - (1 << j) + 1; ++i)
      f[i][j] = min(f[i][j - 1], f[i + (1 << j - 1)][j - 1]);
  }
}
inline int que(int l, int r) { 
  int j = lg[r - l + 1];
  return min(f[l][j], f[r - (1 << j) + 1][j]);
}
 
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();
  init();
  
  auto count = [&](int l, int r) { 
    int sz = r - l + 1;
    l = pos[l];
    int value = 0;
    { // binarySearch left
      int le = 1, ri = l - 1, ret = l;
      while (le <= ri) { 
        int mid = (le + ri) >> 1;
        if (que(mid, l - 1) >= sz) ri = (ret = mid) - 1;
        else le = mid + 1;
      }
      
      value -= ret - 1;
    }
 
    { //binarySearch right
      int le = l, ri = n - 1, ret = l;
      while (le <= ri) { 
        int mid = (le + ri) >> 1;
        if (que(l, mid) >= sz) le = ret = mid + 1;
        else ri = mid - 1;
      }
 
      value += ret;
    }
    return value;
  };
  
  long long answer = 0;
  for (int mid1 = 1; mid1 <= n; ++mid1) { 
    for (int mid2 = mid1; mid2 <= min(n, mid1 + 1); ++mid2) { 
      if (!chk(mid1, mid2)) continue;
      
      int sz = min(mid1, n - mid2);
      int l = 0, r = sz, ret = 0;
      while (l <= r) { 
        int mid = (l + r) >> 1;
 
        if (chk(mid1 - mid, mid2 + mid)) l = (ret = mid) + 1;
        else r = mid - 1;
      }
      
      answer = max(answer, 1ll * count(mid1 - ret, mid2 + ret) * (mid2 - mid1 + 2 * ret + 1));
    }
  }
  
  cout << answer << "\n";
}

Compilation message (stderr)

palindrome.cpp: In function 'void init()':
palindrome.cpp:72:48: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
   72 |       f[i][j] = min(f[i][j - 1], f[i + (1 << j - 1)][j - 1]);
      |                                              ~~^~~

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