Submission #503756

#	Time	Username	Problem	Language	Result	Execution time	Memory
503756		tabr	Islands (IOI08_islands)	C++17	0 / 100	448 ms	98200 KiB

islands

#include <bits/stdc++.h>
using namespace std;
#ifdef tabr
#include "library/debug.cpp"
#else
#define debug(...)
#endif

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<vector<int>> g(n);
    vector<int> l(n);
    vector<int> e(n);
    for (int i = 0; i < n; i++) {
        int j;
        cin >> j >> l[i];
        j--;
        e[i] = j;
        g[i].emplace_back(i);
        g[j].emplace_back(i);
    }
    for (int i = 0; i < n; i++) {
        if (e[e[i]] == i) {
            l[e[i]] = l[i] = max(l[e[i]], l[i]);
        }
    }
    long long ans = 0;
    vector<int> was(n);
    vector<int> pv(n);
    vector<int> cycle(n);
    vector<int> last_id(n);
    for (int i = 0; i < n; i++) {
        if (was[i]) {
            continue;
        }
        int c1 = -1, c2 = -1;
        int sz = 0;
        int dead = -1;
        pv[i] = -1;
        {  // dfs1
            stack<pair<int, int>> stk;
            stk.emplace(i, -1);
            while (!stk.empty()) {
                auto [v, pe] = stk.top();
                if (last_id[v] == (int) g[v].size()) {
                    for (auto id : g[v]) {
                        int to = v ^ id ^ e[id];
                        if (to == pv[v]) {
                            continue;
                        }
                        cycle[v] += cycle[to];
                    }
                    sz += cycle[v];
                    stk.pop();
                    continue;
                }
                for (int gid = last_id[v]; gid < (int) g[v].size(); gid++) {
                    int id = g[v][gid];
                    last_id[v]++;
                    if (id == pe) {
                        continue;
                    }
                    int to = v ^ id ^ e[id];
                    if (was[to]) {
                        if (c1 != -1) {
                            continue;
                        }
                        dead = id;
                        c1 = v;
                        c2 = to;
                        cycle[v]++;
                        if (pv[to] != -1) {
                            cycle[pv[to]]--;
                        }
                        continue;
                    }
                    pv[to] = v;
                    stk.emplace(to, id);
                    break;
                }
            }
        }
        vector<long long> d1(sz + 1), d2(sz + 1);
        function<void(int, int, int, long long)> dfs2 = [&](int v, int p, int cnt, long long now) {
            cnt += cycle[v];
            d1[cnt] = max(d1[cnt], now);
            for (auto id : g[v]) {
                int to = v ^ id ^ e[id];
                if (to == p || id == dead) {
                    continue;
                }
                dfs2(to, v, cnt, now + l[id]);
            }
        };
        dfs2(c1, c2, 0, 0);
        swap(d1, d2);
        dfs2(c2, c1, 0, 0);
        swap(d1, d2);
        for (int j = 0; j < sz; j++) {
            d1[j + 1] = max(d1[j + 1], d1[j]);
            d2[j + 1] = max(d2[j + 1], d2[j]);
        }
        long long t = 0;
        function<long long(int, int, long long)> dfs3 = [&](int v, int p, long long now) {
            vector<long long> c;
            for (auto id : g[v]) {
                int to = v ^ id ^ e[id];
                if (to == p || id == dead) {
                    continue;
                }
                c.emplace_back(dfs3(to, v, now + l[id]));
            }
            t = max(t, now);
            if (c.empty()) {
                return now;
            }
            sort(c.rbegin(), c.rend());
            if (c.size() > 1) {
                t = max(t, c[0] + c[1] - 2 * now);
            }
            return c[0];
        };
        dfs3(c1, c2, 0);
        dfs3(c2, c1, 0);
        debug(t);
        debug(d1);
        debug(d2);
        for (int j = 1; j < sz; j++) {
            t = max(t, d1[j] + d2[sz - j] + l[dead]);
        }
        ans += t;
    }
    cout << ans << '\n';
    return 0;
}

• Subtask 1: 0 / 33
• Subtask 2: 0 / 3
• Subtask 3: 0 / 4
• Subtask 4: 0 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10