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Submission #198383

# Submission time Handle Problem Language Result Execution time Memory
198383 2020-01-25T18:16:58 Z alrad Lampice (COCI19_lampice) C++17
42 / 110
 5000 ms 5632 KB 
#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long ull;

const int N = 5e4 + 2;

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

vector<bool> lf(N , false);

void dfs1(int v , int p = -1) {
   walk.push_back(all[v - 1]);
   if (lf[v]) {
      int cur = getMaxPalindromic(walk);
      ans = max(ans , cur);
   }
   for (int to : g[v]) {
      if (to != p) {
         dfs1(to , v);
         walk.pop_back();
      }
   }
}

int main() {
   ios_base :: sync_with_stdio(0);
   cin.tie(0) , cout.tie(0);
   int n;
   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;
   }
   vector<int> leafs;
   for (int i = 1; i <= n; i++) {
      if ((int)g[i].size() == 1) {
         leafs.push_back(i);
         lf[i] = true;
      }
   }
   for (int i = 0; i < (int)leafs.size(); i++) {
      walk = "";
      dfs1(leafs[i]);
   }
   cout << ans << '\n';
   return 0;
}

Subtask #1
17.0 / 17.0

# Verdict Execution time Memory Grader output
1 Correct 15 ms 1528 KB Output is correct
2 Correct 56 ms 1656 KB Output is correct
3 Correct 479 ms 1784 KB Output is correct
4 Correct 1237 ms 1656 KB Output is correct
5 Correct 3 ms 1528 KB Output is correct
6 Correct 3 ms 1532 KB Output is correct
7 Correct 3 ms 1528 KB Output is correct

Subtask #2
25.0 / 25.0

# Verdict Execution time Memory Grader output
1 Correct 33 ms 4512 KB Output is correct
2 Correct 24 ms 4720 KB Output is correct
3 Correct 26 ms 4724 KB Output is correct
4 Correct 37 ms 4892 KB Output is correct
5 Correct 38 ms 5104 KB Output is correct
6 Correct 37 ms 5104 KB Output is correct

Subtask #3
0 / 31.0

# Verdict Execution time Memory Grader output
1 Execution timed out 5038 ms 5632 KB Time limit exceeded
2 Halted 0 ms 0 KB -

Subtask #4
0 / 37.0

# Verdict Execution time Memory Grader output
1 Correct 15 ms 1528 KB Output is correct
2 Correct 56 ms 1656 KB Output is correct
3 Correct 479 ms 1784 KB Output is correct
4 Correct 1237 ms 1656 KB Output is correct
5 Correct 3 ms 1528 KB Output is correct
6 Correct 3 ms 1532 KB Output is correct
7 Correct 3 ms 1528 KB Output is correct
8 Correct 33 ms 4512 KB Output is correct
9 Correct 24 ms 4720 KB Output is correct
10 Correct 26 ms 4724 KB Output is correct
11 Correct 37 ms 4892 KB Output is correct
12 Correct 38 ms 5104 KB Output is correct
13 Correct 37 ms 5104 KB Output is correct
14 Execution timed out 5038 ms 5632 KB Time limit exceeded
15 Halted 0 ms 0 KB -