Submission #503771

#	Time	Username	Problem	Language	Result	Execution time	Memory
503771		tabr	Islands (IOI08_islands)	C++17	0 / 100	2098 ms	130248 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);
    vector<vector<long long>> c(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();
                was[v] = 1;
                debug(v);
                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];
                    }
                    if (v == c1 || v == c2) {
                        cycle[v] = 1;
                    }
                    sz += cycle[v];
                    stk.pop();
                    continue;
                }
                int &gid = last_id[v];
                while (gid < (int) g[v].size()) {
                    int id = g[v][gid++];
                    if (id == pe) {
                        continue;
                    }
                    int to = v ^ id ^ e[id];
                    if (was[to]) {
                        debug(v, 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);
        for (int z = 0; z < 2; z++) {
            queue<tuple<int, int, int, long long>> que;
            que.emplace(c1, c2, 0, 0);
            while (!que.empty()) {
                auto [v, p, cnt, now] = que.front();
                que.pop();
                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;
                    }
                    que.emplace(to, v, cnt, now + l[id]);
                }
            };
            // dfs2(c1, c2, 0, 0);
            swap(c1, c2);
            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;
        for (int z = 0; z < 2; z++) {
            stack<tuple<int, int, long long>> stk;
            stk.emplace(c1, c2, 0);
            while (!stk.empty()) {
                auto [v, p, now] = stk.top();
                t = max(t, now);
                if (last_id[v] == 0) {
                    stk.pop();
                    if (c[v].empty()) {
                        if (p != c2) {
                            c[p].emplace_back(now);
                        }
                        continue;
                    }
                    sort(c[v].rbegin(), c[v].rend());
                    if (c[v].size() > 1) {
                        t = max(t, c[v][0] + c[v][1] - 2 * now);
                    }
                    long long res = c[v][0];
                    c[v].clear();
                    if (p != c2) {
                        c[p].emplace_back(res);
                    }
                    continue;
                }
                int &gid = last_id[v];
                while (gid >= 0) {
                    gid--;
                    int id = g[v][gid];
                    int to = v ^ id ^ e[id];
                    if (to == p || id == dead) {
                        continue;
                    }
                    stk.emplace(to, v, now + l[id]);
                    c[v].emplace_back();
                }
            };
            swap(c1, c2);
        }
        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