Submission #563627

#	Time	Username	Problem	Language	Result	Execution time	Memory
563627		brunovsky	Bridges (APIO19_bridges)	C++17	100 / 100	2609 ms	14448 KiB

bridges

#include <bits/stdc++.h>
#ifdef LOCAL
#include "code/formatting.hpp"
#else
#define debug(...) (void)0
#endif

using namespace std;

struct disjoint_set_rollback {
    int N, S;
    vector<int> next;
    vector<pair<int, int>> history;

    explicit disjoint_set_rollback(int N = 0) : N(N), S(N), next(N, -1) {}

    void assign(int n) { *this = disjoint_set_rollback(n); }
    void reset() { *this = disjoint_set_rollback(N); }
    bool same(int i, int j) { return find(i) == find(j); }
    bool unit(int i) { return next[i] == -1; }
    bool root(int i) { return next[i] < 0; }
    int size(int i) { return -next[i]; }
    int time() const { return history.size(); }

    void rollback(int t) {
        int i = time();
        while (i > t) {
            i--, next[history[i].first] = history[i].second;
            i--, next[history[i].first] = history[i].second;
            S++;
        }
        history.resize(t);
    }

    int find(int i) {
        while (next[i] >= 0) {
            i = next[i];
        }
        return i;
    }

    bool join(int i, int j) {
        i = find(i);
        j = find(j);
        if (i != j) {
            if (size(i) < size(j)) {
                swap(i, j);
            }
            history.emplace_back(i, next[i]);
            history.emplace_back(j, next[j]);
            next[i] += next[j];
            next[j] = i, S--;
            return true;
        }
        return false;
    }
};

auto filter_pairs(const vector<array<int, 2>>& a) {
    int N = a.size();
    vector<array<int, 2>> b;
    for (int i = 0; i < N; i++) {
        if (i == 0 || a[i][0] != a[i - 1][0]) {
            b.push_back(a[i]);
        }
    }
    return b;
}

int main() {
    ios::sync_with_stdio(false), cin.tie(nullptr);
    int N, M;
    cin >> N >> M;
    vector<array<int, 3>> graph(M);
    for (int i = 0; i < M; i++) {
        int u, v, d;
        cin >> u >> v >> d, u--, v--;
        graph[i] = {d, u, v};
    }

    auto edge_compare = [&](int a, int b) {
        return make_pair(graph[a][0], a) > make_pair(graph[b][0], b);
    };
    set<int, decltype(edge_compare)> edges(edge_compare);
    for (int e = 0; e < M; e++) {
        edges.insert(e);
    }

    int Q;
    cin >> Q;
    vector<array<int, 3>> queries(Q);
    for (int q = 0; q < Q; q++) {
        int t, a, b;
        cin >> t >> a >> b, a--;
        queries[q] = {t, a, b};
    }

    const int B = sqrt(2 * N + Q);
    vector<int> ans(Q), weight(M);

    for (int L = 0, R = min(B, Q); L < Q; L = R, R = min(Q, R + B)) {
        vector<int> upds, asks;
        vector<array<int, 2>> bans;
        for (int q = L; q < R; q++) {
            auto [t, a, b] = queries[q];
            if (t == 1) {
                upds.push_back(q);
                bans.push_back({a, q});
                weight[a] = -1;
            } else if (t == 2) {
                asks.push_back(q);
            } else {
                assert(false);
            }
        }

        sort(begin(asks), end(asks), [&](int i, int j) {
            return make_pair(queries[i][2], j) > make_pair(queries[j][2], i);
        });

        sort(begin(bans), end(bans));
        bans = filter_pairs(bans);

        for (auto [e, _] : bans) {
            edges.erase(e);
        }

        disjoint_set_rollback dsu(N);

        auto it = edges.begin();
        int U = upds.size();

        for (int q : asks) {
            auto [tq, s, w] = queries[q];
            while (it != edges.end() && graph[*it][0] >= w) {
                auto [_, a, b] = graph[*it++];
                dsu.join(a, b);
            }
            int time = dsu.time();
            for (int u = 0; u < U && upds[u] < q; u++) {
                auto [_, e, c] = queries[upds[u]];
                weight[e] = c;
            }
            for (auto [e, t] : bans) {
                int c = q < t ? graph[e][0] : weight[e];
                auto [_, a, b] = graph[e];
                if (c >= w) {
                    dsu.join(a, b);
                }
            }
            ans[q] = dsu.size(dsu.find(s));
            dsu.rollback(time);
        }

        for (int q : upds) {
            auto [_, e, w] = queries[q];
            edges.erase(e), graph[e][0] = w, edges.insert(e);
            weight[e] = 0;
        }
    }

    for (int q = 0; q < Q; q++) {
        if (ans[q] > 0) {
            cout << ans[q] << '\n';
        }
    }

    return 0;
}

// sqrt rebuilds

• Subtask 1: 13 / 13
• Subtask 2: 16 / 16
• Subtask 3: 17 / 17
• Subtask 4: 14 / 14
• Subtask 5: 13 / 13
• Subtask 6: 27 / 27