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Submission #530829

# Submission time Handle Problem Language Result Execution time Memory
530829 2022-02-26T22:06:29 Z Alex_tz307 Lampice (COCI19_lampice) C++17
42 / 110
 5000 ms 14164 KB 
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

using namespace std;

const int kN = 5e4;
const int mod = 1e9 + 7;
const int base = 29;
string s;
vector<int> g[1 + kN];
int len, m, p[1 + kN], sz[1 + kN], h1[1 + kN], h2[1 + kN], nodes[1 + kN];
vector<int> centroids;
bitset<1 + kN> vis;
unordered_multiset<int> preffixes[kN];

int add(int x, int y) {
  x += y;
  if (x >= mod) {
    return x - mod;
  }
  return x;
}

int mult(int x, int y) {
  return (int64_t)x * y % mod;
}

void precalc() {
  p[0] = 1;
  for (int i = 1; i <= kN; ++i) {
    p[i] = mult(p[i - 1], base);
  }
}

void findSize(int u, int par) {
  sz[u] = 1;
  for (int v : g[u]) {
    if (!vis[v] && v != par) {
      findSize(v, u);
      sz[u] += sz[v];
    }
  }
}

int findCentroid(int u, int par, int n) {
  for (int v : g[u]) {
    if (!vis[v] && v != par && sz[v] > n / 2) {
      return findCentroid(v, u, n);
    }
  }
  return u;
}

void build(int u) {
  findSize(u, 0);
  int c = findCentroid(u, 0, sz[u]);
  centroids.emplace_back(c);
  vis[c] = true;
  for (int v : g[c]) {
    if (!vis[v]) {
      build(v);
    }
  }
}

void dfs1(int u, int par, int depth) {
  h1[u] = add(mult(h1[par], base), s[u] - 'a' + 1);
  h2[u] = add(h2[par], mult(p[depth], s[u] - 'a' + 1));
  preffixes[depth + 1].emplace(h1[u]);
  for (int v : g[u]) {
    if (!vis[v] && v != par) {
      dfs1(v, u, depth + 1);
    }
  }
}

void addPaths(int u, int par, int depth) {
  preffixes[depth].emplace(h1[u]);
  for (int v : g[u]) {
    if (!vis[v] && v != par) {
      addPaths(v, u, depth + 1);
    }
  }
}

void removePaths(int u, int par, int depth) {
  preffixes[depth].erase(preffixes[depth].find(h1[u]));
  for (int v : g[u]) {
    if (!vis[v] && v != par) {
      removePaths(v, u, depth + 1);
    }
  }
}

bool dfs2(int u, int par, int depth) {
  if (depth == len) {
    return h1[u] == h2[u];
  }
  nodes[m++] = u;
  int d = len - depth + 1;
  if (d <= depth) {
    int split = nodes[m - d];
    if (h1[split] == h2[split]) {
      split = nodes[m - d - 1];
      int hsh = add(h1[u], mod - mult(p[d], h1[split]));
      if (preffixes[d].count(hsh)) {
        return true;
      }
    }
  }
  for (int v : g[u]) {
    if (!vis[v] && v != par && dfs2(v, u, depth + 1)) {
      return true;
    }
  }
  m -= 1;
  return false;
}

bool solve(int u) {
  for (int c : centroids) {
    vis[c] = true;
    dfs1(c, 0, 0);
    for (int v : g[c]) {
      if (!vis[v]) {
        removePaths(v, c, 2);
        m = 0;
        nodes[m++] = 0;
        nodes[m++] = c;
        if (dfs2(v, c, 2)) {
          addPaths(v, c, 2);
          removePaths(c, 0, 1);
          return true;
        }
        addPaths(v, c, 2);
      }
    }
    removePaths(c, 0, 1);
  }
  return false;
}

bool check(int n) {
  bool ret = solve(1);
  for (int v = 1; v <= n; ++v) {
    vis[v] = false;
  }
  return ret;
}

void testCase() {
  int n;
  cin >> n >> s;
  s = '$' + s;
  bool ok2 = false;
  for (int i = 1; i < n; ++i) {
    int u, v;
    cin >> u >> v;
    g[u].emplace_back(v);
    g[v].emplace_back(u);
    if (s[u] == s[v]) {
      ok2 = true;
    }
  }
  build(1);
  for (int v = 1; v <= n; ++v) {
    vis[v] = false;
  }
  int l = 1, r = (n - 1) / 2, ans1 = 1;
  while (l <= r) {
    int mid = (l + r) / 2;
    len = 2 * mid + 1;
    if (check(n)) {
      ans1 = 2 * mid + 1;
      l = mid + 1;
    } else {
      r = mid - 1;
    }
  }
  int ans2 = 0;
  l = 2, r = n / 2;
  while (l <= r) {
    int mid = (l + r) / 2;
    len = 2 * mid;
    if (check(n)) {
      ans2 = 2 * mid;
      l = mid + 1;
    } else {
      r = mid - 1;
    }
  }
  cout << max({1 + ok2, ans1, ans2}) << '\n';
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  precalc();
  int tests = 1;
  for (int tc = 0; tc < tests; ++tc) {
    testCase();
  }
  return 0;
}

Subtask #1
17.0 / 17.0

# Verdict Execution time Memory Grader output
1 Correct 8 ms 4428 KB Output is correct
2 Correct 15 ms 4428 KB Output is correct
3 Correct 48 ms 4556 KB Output is correct
4 Correct 84 ms 4616 KB Output is correct
5 Correct 3 ms 4432 KB Output is correct
6 Correct 4 ms 4428 KB Output is correct
7 Correct 3 ms 4428 KB Output is correct

Subtask #2
25.0 / 25.0

# Verdict Execution time Memory Grader output
1 Correct 3173 ms 12820 KB Output is correct
2 Correct 2329 ms 13028 KB Output is correct
3 Correct 1404 ms 13256 KB Output is correct
4 Correct 1775 ms 13712 KB Output is correct
5 Correct 2959 ms 14144 KB Output is correct
6 Correct 285 ms 14164 KB Output is correct

Subtask #3
0 / 31.0

# Verdict Execution time Memory Grader output
1 Execution timed out 5082 ms 10540 KB Time limit exceeded
2 Halted 0 ms 0 KB -

Subtask #4
0 / 37.0

# Verdict Execution time Memory Grader output
1 Correct 8 ms 4428 KB Output is correct
2 Correct 15 ms 4428 KB Output is correct
3 Correct 48 ms 4556 KB Output is correct
4 Correct 84 ms 4616 KB Output is correct
5 Correct 3 ms 4432 KB Output is correct
6 Correct 4 ms 4428 KB Output is correct
7 Correct 3 ms 4428 KB Output is correct
8 Correct 3173 ms 12820 KB Output is correct
9 Correct 2329 ms 13028 KB Output is correct
10 Correct 1404 ms 13256 KB Output is correct
11 Correct 1775 ms 13712 KB Output is correct
12 Correct 2959 ms 14144 KB Output is correct
13 Correct 285 ms 14164 KB Output is correct
14 Execution timed out 5082 ms 10540 KB Time limit exceeded
15 Halted 0 ms 0 KB -