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Submission #198379

# Submission time Handle Problem Language Result Execution time Memory
198379 2020-01-25T17:51:47 Z alrad Lampice (COCI19_lampice) C++17
42 / 110
 1188 ms 5744 KB 
#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long ull;

const int N = 5e4 + 2;

int n;
vector<vector<int> > g(N , vector<int>());
int ans = 0;
string all;
string walk = "";

bool good(string cur) {
   string other = cur;
   reverse(other.begin() , other.end());
   return other == cur;
}

void dfs(int v , int p = -1) {
   walk.push_back(all[v - 1]);
   if (good(walk)) {
      ans = max(ans , (int)walk.size());
   }
   for (int to : g[v]) {
      if (to != p) {
         dfs(to , v);
         walk.pop_back();
      }
   }
}

//hashing

int gen_base(const int before , const int after) {
   auto seed = chrono::high_resolution_clock::now().time_since_epoch().count();
   mt19937 mt_rand(seed);
   int base = uniform_int_distribution<int>(before + 1, after)(mt_rand);
   return base % 2 == 0 ? base - 1 : base;
}

struct PolyHash {
   static const int mod = (int)1e9 + 123;
   static vector<int> pow1;
   static vector<ull> pow2;
   static int base;

   static inline int diff(int a , int b) {
      return (a -= b) < 0 ? a + mod : a;
   }

   vector<int> pref1;
   vector<ull> pref2;

   PolyHash(const string s) : pref1(s.size() + 1u , 0) , pref2(s.size() + 1u , 0) {
      assert(base < mod);
      const int n = s.size();
      while ((int)pow1.size() <= n) {
         pow1.push_back(1LL * pow1.back() * base % mod);
         pow2.push_back(pow2.back() * base);
      }
      for (int i = 0; i < n; i++) {
         assert(base > s[i]);
         pref1[i + 1] = (pref1[i] + 1LL * s[i] * pow1[i]) % mod;
         pref2[i + 1] = pref2[i] + s[i] * pow2[i];
      }
   }

   inline pair<int , ull> operator()(const int pos , const int len , const int mxPow = 0) const {
      int hash1 = pref1[pos + len] - pref1[pos];
      ull hash2 = pref2[pos + len] - pref2[pos];
      if (hash1 < 0) hash1 += mod;
      if (mxPow != 0) {
         hash1 = 1LL * hash1 * pow1[mxPow - (pos + len - 1)] % mod;
         hash2 *= pow2[mxPow - (pos + len - 1)];
      }
      return make_pair(hash1 , hash2);
   }
};

int PolyHash::base((int)1e9 + 7);
vector<int> PolyHash::pow1{1};
vector<ull> PolyHash::pow2{2};

int getMaxPalindromic(string a) {
   int result = 0;
   PolyHash::base = gen_base(256 , PolyHash::mod);
   string b(a);
   reverse(b.begin() , b.end());
   PolyHash hash_a(all) , hash_b(b);
   for (int i = 0 , j = n - 1; i < n; i++ , j--) {
      int low = 0 , high = min(n - i , n - j) + 1;
      while (high - low > 1) {
         int mid = (low + high) >> 1;
         if (hash_a(i , mid , n) == hash_b(j , mid , n)) {
            low = mid;
         } else {
            high = mid;
         }
      }
      result = max(result , 2 * low - 1);
      low = 0 , high = min(n - i - 1 , n - j) + 1;
      while (high - low > 1) {
         int mid = (high + low) >> 1;
         if (hash_a(i + 1 , mid , n) == hash_b(j , mid , n)) {
            low = mid;
         } else {
            high = mid;
         }
      }
      result = max(result , 2 * low);
   }
   return result;
}

int main() {
   ios_base :: sync_with_stdio(0);
   cin.tie(0) , cout.tie(0);
   cin >> n;
   cin >> all;
   bool subtask2 = true;
   for (int i = 1; i < n; i++) {
      int u , v;
      cin >> u >> v;
      if (u + 1 != v) {
         subtask2 = false;
      }
      g[u].push_back(v);
      g[v].push_back(u);
   }
   if (n <= 3000) {
      //solve subtask 1
      for (int i = 1; i <= n; i++) {
         walk = "";
         dfs(i);
      }
      cout << ans << '\n';
      return 0;
   }
   if (subtask2) {
      //solve subtask 2
      cout << getMaxPalindromic(all) << '\n';
      return 0;
   }
   return 0;
}

Subtask #1
17.0 / 17.0

# Verdict Execution time Memory Grader output
1 Correct 14 ms 1656 KB Output is correct
2 Correct 59 ms 1528 KB Output is correct
3 Correct 479 ms 1784 KB Output is correct
4 Correct 1188 ms 1656 KB Output is correct
5 Correct 3 ms 1532 KB Output is correct
6 Correct 7 ms 1528 KB Output is correct
7 Correct 2 ms 1528 KB Output is correct

Subtask #2
25.0 / 25.0

# Verdict Execution time Memory Grader output
1 Correct 32 ms 5148 KB Output is correct
2 Correct 33 ms 5232 KB Output is correct
3 Correct 34 ms 5332 KB Output is correct
4 Correct 35 ms 5504 KB Output is correct
5 Correct 42 ms 5692 KB Output is correct
6 Correct 38 ms 5744 KB Output is correct

Subtask #3
0 / 31.0

# Verdict Execution time Memory Grader output
1 Incorrect 29 ms 3704 KB Output isn't correct
2 Halted 0 ms 0 KB -

Subtask #4
0 / 37.0

# Verdict Execution time Memory Grader output
1 Correct 14 ms 1656 KB Output is correct
2 Correct 59 ms 1528 KB Output is correct
3 Correct 479 ms 1784 KB Output is correct
4 Correct 1188 ms 1656 KB Output is correct
5 Correct 3 ms 1532 KB Output is correct
6 Correct 7 ms 1528 KB Output is correct
7 Correct 2 ms 1528 KB Output is correct
8 Correct 32 ms 5148 KB Output is correct
9 Correct 33 ms 5232 KB Output is correct
10 Correct 34 ms 5332 KB Output is correct
11 Correct 35 ms 5504 KB Output is correct
12 Correct 42 ms 5692 KB Output is correct
13 Correct 38 ms 5744 KB Output is correct
14 Incorrect 29 ms 3704 KB Output isn't correct
15 Halted 0 ms 0 KB -