Submission #934501

#	Time	Username	Problem	Language	Result	Execution time	Memory
934501		MisterReaper	Railway (BOI17_railway)	C++17	100 / 100	98 ms	27340 KiB

railway

#include <bits/stdc++.h>
using i64 = long long;

void solve() {
    int n, m, k;
    std::cin >> n >> m >> k;

    std::vector adj(n, std::vector<std::pair<int, int>> ());
    for(int i = 0; i < n - 1; i++) {
        int u, v;
        std::cin >> u >> v;
        adj[--u].emplace_back(--v, i);
        adj[v].emplace_back(u, i);
    }

    const int L = std::__lg(n) + 2;

    int timer = 0;
    std::vector par(n, std::vector<int> (L));
    std::vector<int> tin(n), tout(n), dep(n), val(n), pedge(n);
    auto dfs = [&](auto&& self, int node, int p) -> void {
        tin[node] = timer++;
        par[node][0] = p;
        for(auto [child, idx] : adj[node]) {
            if(child == p) {
                continue;
            }
            pedge[child] = idx;
            dep[child] = dep[node] + 1;
            self(self, child, node);
        }
        tout[node] = timer++;
    };

    dfs(dfs, 0, 0);

    for(int lg = 1; lg < L; lg++) {
        for(int i = 0; i < n; i++) {
            par[i][lg] = par[par[i][lg - 1]][lg - 1];
        }
    }

    std::vector s(m, std::vector<int> ());
    for(int i = 0; i < m; i++) {
        int x;
        std::cin >> x;
        s[i].resize(x);
        for(int j = 0; j < x; j++) {
            std::cin >> s[i][j];
            s[i][j]--;
        }
        std::sort(s[i].begin(), s[i].end(), [&](int lhs, int rhs) -> bool {
            return tin[lhs] < tin[rhs];
        });
        s[i].emplace_back(s[i].front());
    }

    auto get = [&](int node, int l) -> int {
        for(int lg = L - 1; lg >= 0; lg--) {
            if(l >> lg & 1) {
                node = par[node][lg];
            }
        }

        return node;
    };

    auto lca = [&](int a, int b) -> int {
        if(dep[b] > dep[a]) {
            std::swap(a, b);
        }

        a = get(a, dep[a] - dep[b]);
        for(int lg = L - 1; lg >= 0; lg--) {
            if(par[a][lg] != par[b][lg]) {
                a = par[a][lg];
                b = par[b][lg];
            }
        }

        return (a == b ? a : par[a][0]);
    };

    for(int i = 0; i < m; i++) {
        int x = int(s[i].size());
        for(int j = 0; j + 1 < x; j++) {
            int u = s[i][j], v = s[i][j + 1];
            int g = lca(u, v);
            //std::cerr << u << " " << v << " :: " << g << "\n";
            val[u]++;
            val[v]++;
            val[g] -= 2;
        }
    }

    /*
    for(int i = 0; i < n; i++) {
        std::cerr << val[i] << " \n"[i == n - 1];
    }
    */

    auto dfs2 = [&](auto&& self, int node, int p) -> void {
        for(auto [child, idx] : adj[node]) {
            if(child == p) {
                continue;
            }
            self(self, child, node);
            val[node] += val[child];
        }
    };

    dfs2(dfs2, 0, 0);

    std::vector<int> ans;
    for(int i = 0; i < n; i++) {
        //std::cerr << val[i] << " \n"[i == n - 1];
        if(val[i] >= 2 * k) {
            ans.emplace_back(pedge[i]);
        }
    }

    std::sort(ans.begin(), ans.end());
    std::cout << int(ans.size()) << "\n";
    for(int i = 0; i < int(ans.size()); i++) {
        std::cout << ans[i] + 1 << " ";
    }
    
    return;
}

signed main() {
    #ifdef LOCAL
        freopen("in.txt", "r", stdin);
        freopen("out.txt", "w", stdout);
    #endif

    std::ios_base::sync_with_stdio(false);
    std::cin.tie(NULL); std::cout.tie(NULL);

    int t = 1; //std::cin >> t;
    for(int i = 1; i <= t; i++) {
        solve();
    }

    return 0;
}

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 7 / 7
• Subtask 4: 29 / 29
• Subtask 5: 16 / 16
• Subtask 6: 25 / 25