Submission #676295

#	Time	Username	Problem	Language	Result	Execution time	Memory
676295		vuavisao	Lampice (COCI19_lampice)	C++14	110 / 110	4365 ms	12184 KiB

lampice

#include<bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define ll long long
using namespace std;

template<typename Lhs, typename Rhs> inline void Max_self(Lhs &a, Rhs b) { a = (a > b ? a : b); }
template<typename Lhs, typename Rhs> inline void Min_self(Lhs &a, Rhs b) { a = (a < b ? a : b); }

const int N = 5e4 + 10;
const int MOD = 1e9 + 7;
const int BASE = 128;

int n;
string s;
vector<int> g[N];

int cnt_node, child[N];
bool rem[N];

int cap;
int pw[N], up[N], down[N];
vector<int> odd, even;

int res = 1;

void dfs_child(int u, int p) {
    ++ cnt_node;
    child[u] = 1;
    for(const auto& v : g[u]) {
        if(v == p || rem[v]) continue;
        dfs_child(v, u);
        child[u] += child[v];
    }
}

int dfs_centroid(int u, int p) {
    for(const auto& v : g[u]) {
        if(v == p || rem[v]) continue;
        if(child[v] > cnt_node / 2) return dfs_centroid(v, u);
    }
    return u;
}

int get_hash(int l, int r) {
    if(l == 0) return down[r];
    return (0ll + down[r] - 1ll * down[l - 1] * pw[r - l + 1] + 1ll * MOD * MOD) % MOD;
}

bool split(int u, int p) {
    cnt_node = 0; dfs_child(u, p);
    u = dfs_centroid(u, p);
    rem[u] = true;

    down[0] = up[0] = s[u] - 'a' + 1;
    unordered_set<int> stt = {};
    function<void(int, int, int)> add = [&] (int u, int p, int len) {
        if(len + 1 > cap) return;
        down[len] = (1ll * down[len - 1] * BASE + s[u] - 'a' + 1) % MOD;
        stt.insert(down[len]);
        for(const auto& v : g[u]) {
            if(v == p || rem[v]) continue;
            add(v, u, len + 1);
        }
    };

    bool have = false;
    function<void(int, int, int)> calc = [&] (int u, int p, int len) {
        if(have || len + 1 > cap) return;
        down[len] = (1ll * down[len - 1] * BASE + s[u] - 'a' + 1) % MOD;
        up[len] = (1ll * up[len - 1] + 1ll * (s[u] - 'a' + 1) * pw[len]) % MOD;
        if(len + 1 == cap) {
            if(up[len] == down[len]) {
                have = true;
                return;
            }
        }
        if(2 * (len + 1) > cap) {
            int use_palin = 2 * (len + 1) - cap - 1;
            if(down[use_palin] == up[use_palin]) {
                int hash = get_hash(use_palin, len);
                if(stt.find(hash) != stt.end()) {
                    have = true;
                    return;
                }
            }
        }
        for(const auto& v : g[u]) {
            if(v == p || rem[v]) continue;
            calc(v, u, len + 1);
        }
    };

    for(const auto& v : g[u]) {
        if(rem[v]) continue;
        calc(v, u, 1);
        if(have) return true;
        add(v, u, 1);
    }

    stt.clear();
    reverse(g[u].begin(), g[u].end());

    for(const auto& v : g[u]) {
        if(rem[v]) continue;
        calc(v, u, 1);
        if(have) return true;
        add(v, u, 1);
    }

    for(const auto& v : g[u]) {
        if(rem[v]) continue;
        if(split(v, u)) return true;
    }
    return false;
}

void solve(bool ODD) {
    const auto& s = (ODD ? odd : even);
    int l = 0, r = (int) s.size() - 1;
    while(l <= r) {
        int mid = (l + r) >> 1;
        cap = s[mid];
        memset(rem, false, sizeof(rem));
        if(split(1, 0)) {
            Max_self(res, cap);
            l = mid + 1;
        }
        else {
            r = mid - 1;
        }
    }
}

int32_t main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    if (fopen("COCI19_lampice.inp", "r")) {
        freopen("COCI19_lampice.inp", "r", stdin);
        freopen("COCI19_lampice.out", "w", stdout);
    }
    cin >> n >> s; s = ' ' + s;
    for(int i = 2; i <= n; ++ i) {
        int u, v; cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    pw[0] = 1;
    for(int i = 1; i <= n; ++ i) {
        pw[i] = 1ll * pw[i - 1] * BASE % MOD;
        if(i & 1) {
            if(i > 1) {
                odd.push_back(i);
            }
        }
        else {
            even.push_back(i);
        }
    }
    solve(0); solve(1);
    cout << res;
    return 0;
}

/// Code by vuavisao

Compilation message (stderr)

lampice.cpp: In function 'int32_t main()':
lampice.cpp:140:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  140 |         freopen("COCI19_lampice.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
lampice.cpp:141:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  141 |         freopen("COCI19_lampice.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 17 / 17
• Subtask 2: 25 / 25
• Subtask 3: 31 / 31
• Subtask 4: 37 / 37