Submission #861727

#	Time	Username	Problem	Language	Result	Execution time	Memory
861727		arbuzick	Cat Exercise (JOI23_ho_t4)	C++17	100 / 100	217 ms	63300 KiB

Main

// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("avx,avx2")
#include <bits/stdc++.h>

using namespace std;

struct DSU {
    int n;
    vector<int> sz, p;
    vector<pair<int, int>> mx;

    DSU(int _n, vector<int> vals) {
        n = _n;
        sz.assign(n, 1);
        p.resize(n);
        iota(p.begin(), p.end(), 0);
        mx.resize(n);
        for (int i = 0; i < n; ++i) {
            mx[i] = {vals[i], i};
        }
    }

    int pr(int v) {
        if (p[v] == v) {
            return v;
        }
        return p[v] = pr(p[v]);
    }

    void unite(int a, int b) {
        a = pr(a), b = pr(b);
        if (a == b) {
            return;
        }
        if (sz[a] < sz[b]) {
            swap(a, b);
        }
        p[b] = a;
        sz[a] += sz[b];
        mx[a] = max(mx[a], mx[b]);
    }
};

constexpr int maxn = 2e5 + 5, lg = 20;

vector<int> g[maxn];

int go[lg][maxn];

int tin[maxn], tout[maxn];

int t = 0;

int d[maxn];

void dfs(int v) {
    tin[v] = t;
    t++;
    for (auto u : g[v]) {
        if (u != go[0][v]) {
            go[0][u] = v;
            d[u] = d[v] + 1;
            dfs(u);
        }
    }
    tout[v] = t;
}

int lca(int a, int b) {
    if (tin[a] <= tin[b] && tout[b] <= tout[a]) {
        return a;
    }
    if (tin[b] <= tin[a] && tout[a] <= tout[b]) {
        return b;
    }
    int v = a;
    for (int i = lg - 1; i >= 0; --i) {
        if (!(tin[go[i][v]] <= tin[b] && tout[b] <= tout[go[i][v]])) {
            v = go[i][v];
        }
    }
    return go[0][v];
}

int get_dist(int a, int b) {
    return d[a] + d[b] - d[lca(a, b)] * 2;
}

void solve() {
    int n;
    cin >> n;
    vector<int> p(n);
    vector<pair<int, int>> ord(n);
    for (int i = 0; i < n; ++i) {
        cin >> p[i];
        p[i]--;
        ord[i] = {p[i], i};
    }
    sort(ord.begin(), ord.end());
    for (int i = 0; i < n - 1; ++i) {
        int a, b;
        cin >> a >> b;
        a--, b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    dfs(0);
    for (int i = 1; i < lg; ++i) {
        for (int j = 0; j < n; ++j) {
            go[i][j] = go[i - 1][go[i - 1][j]];
        }
    }
    vector<long long> dp(n);
    vector<vector<int>> updates(n);
    DSU d(n, p);
    for (int i = 0; i < n; ++i) {
        for (auto j : g[ord[i].second]) {
            if (p[j] < ord[i].first) {
                updates[i].push_back(d.mx[d.pr(j)].first);
                d.unite(ord[i].second, j);
            }
        }
    }
    long long ans = 0;
    for (int i = n - 1; i >= 0; --i) {
        for (auto j : updates[i]) {
            dp[j] = max(dp[j], dp[i] + get_dist(ord[i].second, ord[j].second));
            ans = max(ans, dp[j]);
        }
    }
    cout << ans << '\n';
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}

• Subtask 1: 7 / 7
• Subtask 2: 7 / 7
• Subtask 3: 7 / 7
• Subtask 4: 10 / 10
• Subtask 5: 20 / 20
• Subtask 6: 23 / 23
• Subtask 7: 26 / 26