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Submission #198371

# Submission time Handle Problem Language Result Execution time Memory
198371 2020-01-25T17:33:25 Z alrad Lampice (COCI19_lampice) C++17
42 / 110
 1170 ms 5644 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 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
      PolyHash::base = gen_base(256 , PolyHash::mod);
      string b(all);
      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;
            }
         }
         ans = max(ans , 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;
            }
         }
         ans = max(ans , 2 * low);
      }
      cout << ans << '\n';
      return 0;
   }
   return 0;
}

Subtask #1
17.0 / 17.0

# Verdict Execution time Memory Grader output
1 Correct 14 ms 1528 KB Output is correct
2 Correct 52 ms 1528 KB Output is correct
3 Correct 461 ms 1532 KB Output is correct
4 Correct 1170 ms 1656 KB Output is correct
5 Correct 3 ms 1528 KB Output is correct
6 Correct 4 ms 1528 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 27 ms 4592 KB Output is correct
2 Correct 33 ms 5152 KB Output is correct
3 Correct 35 ms 5488 KB Output is correct
4 Correct 34 ms 5488 KB Output is correct
5 Correct 38 ms 5640 KB Output is correct
6 Correct 35 ms 5644 KB Output is correct

Subtask #3
0 / 31.0

# Verdict Execution time Memory Grader output
1 Incorrect 31 ms 3192 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 1528 KB Output is correct
2 Correct 52 ms 1528 KB Output is correct
3 Correct 461 ms 1532 KB Output is correct
4 Correct 1170 ms 1656 KB Output is correct
5 Correct 3 ms 1528 KB Output is correct
6 Correct 4 ms 1528 KB Output is correct
7 Correct 3 ms 1528 KB Output is correct
8 Correct 27 ms 4592 KB Output is correct
9 Correct 33 ms 5152 KB Output is correct
10 Correct 35 ms 5488 KB Output is correct
11 Correct 34 ms 5488 KB Output is correct
12 Correct 38 ms 5640 KB Output is correct
13 Correct 35 ms 5644 KB Output is correct
14 Incorrect 31 ms 3192 KB Output isn't correct
15 Halted 0 ms 0 KB -