Submission #674140

#	Time	Username	Problem	Language	Result	Execution time	Memory
674140		vuavisao	Lampice (COCI19_lampice)	C++14	17 / 110	5084 ms	8296 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];
int parent[N];

int limit;
int pw[N], up[N], down[N];
unordered_map<int, int> mpp;
vector<int> odd, even;

int res = 1;

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

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

/// 0 : add question
/// 1 : query question
bool dfs_calc(int u, int p, int len, int type);
bool dfs_calc(int u, int p, int len, int type) {
    if(len + 1 > limit) return false;
    auto get_hash = [&] (int l, int r) -> ll {
        if(l == 0) return down[r];
        return (1ll * down[r] - 1ll * down[l - 1] * pw[r - l + 1] % MOD + MOD) % MOD;
    };
    down[len] = (1ll * down[len - 1] * BASE + s[u]) % MOD;
    up[len] = (1ll * up[len - 1] + 1ll * s[u] * pw[len]) % MOD;
    if(type == 0) {
        ++ mpp[down[len]];
    }
    else {
        if(len + 1 == limit) {
            if(up[len] == down[len]) return true;
        }
        else {
            if(2 * (len + 1) > limit) {
                ll use_palin = 2 * (len + 1) - limit - 1;
                if(down[use_palin] == up[use_palin]) {
                    int hash = get_hash(use_palin, len);
                    if(mpp.find(hash) != mpp.end()) return true;
                }
            }
        }
    }

    for(const auto& v : g[u]) {
        if(v == p || parent[v]) continue;
        if(dfs_calc(v, u, len + 1, type)) return true;
    }
    return false;
}

bool split(int u, int p);
bool split(int u, int p) {
    cnt_node = 0;
    dfs_child(u, p);
    int centroid = dfs_centroid(u, p);
    if(p == 0) {
        p = centroid;
    }
    parent[centroid] = p;

    down[0] = up[0] = s[centroid];
    for(const auto& v : g[centroid]) {
        if(parent[v]) continue;
        if(dfs_calc(v, centroid, 1, 1)) return true;
        dfs_calc(v, centroid, 1, 0);
    }
    mpp.clear();
    reverse(g[centroid].begin(), g[centroid].end());

    for(const auto& v : g[centroid]) {
        if(parent[v]) continue;
        if(dfs_calc(v, centroid, 1, 1)) return true;
        dfs_calc(v, centroid, 1, 0);
    }
    mpp.clear();

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

void solve(bool ODD);
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;
        mpp.clear();
        for(int i = 0; i <= n; ++ i) {
            parent[i] = 0;
        }
        limit = s[mid];
        if(split(1, 0)) {
            Max_self(res, limit);
            l = mid + 1;
        }
        else {
            r = mid - 1;
        }
    }
}

int32_t main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    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

• Subtask 1: 17 / 17
• Subtask 2: 0 / 25
• Subtask 3: 0 / 31
• Subtask 4: 0 / 37