Submission #658516

#	Time	Username	Problem	Language	Result	Execution time	Memory
658516		borisAngelov	Railway (BOI17_railway)	C++17	100 / 100	176 ms	25556 KiB

railway

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

const int maxn = 100005;
const int logn = 20;

int n, q, k;

vector<pair<int, int>> g[maxn];

int depth[maxn];
int jump[maxn][logn];

int parentEdgeIndex[maxn];
int in[maxn];
int out[maxn];

int timer = 0;

int s;
int cities[maxn];

void dfs(int node, int parent, int dep) {
    in[node] = ++timer;

    depth[node] = dep;

    for (auto [v, idx] : g[node]) {
        if (v != parent) {
            parentEdgeIndex[v] = idx;
            jump[v][0] = node;

            dfs(v, node, dep + 1);
        }
    }

    out[node] = timer;
}

void build_sparse() {
    jump[1][0] = 1;

    for (int i = 1; i < logn; ++i) {
        for (int j = 1; j <= n; ++j) {
            jump[j][i] = jump[jump[j][i - 1]][i - 1];
        }
    }
}

int get_lca(int x, int y) {
    if (depth[x] < depth[y]) swap(x, y);

    int diff = depth[x] - depth[y];

    for (int i = 0; i < logn; ++i) {
        if ((diff & (1 << i)) != 0) {
            x = jump[x][i];
            diff -= (1 << i);

            if (diff == 0) break;
        }
    }

    if (x == y) return x;

    for (int i = logn - 1; i >= 0; --i) {
        if (jump[x][i] != jump[y][i]) {
            x = jump[x][i];
            y = jump[y][i];
        }
    }

    return jump[x][0];
}

bool cmp(int i, int j) {
    return in[i] < in[j];
}

int tree[4 * maxn];

void update(int node, int l, int r, int idx, int delta) {
    if (idx < l || idx > r) return;

    if (l == r) {
        tree[node] += delta;
        return;
    }

    int mid = (l + r) / 2;

    update(node * 2, l, mid, idx, delta);
    update(node * 2 + 1, mid + 1, r, idx, delta);

    tree[node] = tree[node * 2] + tree[node * 2 + 1];
}

int query(int node, int l, int r, int ql, int qr) {
    if (l > qr || r < ql) return 0;
    if (ql <= l && r <= qr) return tree[node];

    int mid = (l + r) / 2;

    return query(node * 2, l, mid, ql, qr) + query(node * 2 + 1, mid + 1, r, ql, qr);
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    cin >> n >> q >> k;

    for (int i = 1; i < n; ++i) {
        int u, v; cin >> u >> v;

        g[u].push_back({v, i});
        g[v].push_back({u, i});
    }

    dfs(1, 0, 1);

    build_sparse();

    while (q--) {
        cin >> s;

        for (int i = 1; i <= s; ++i) {
            cin >> cities[i];
        }

        sort(cities + 1, cities + s + 1, cmp);

        cities[s + 1] = cities[1];

        for (int i = 1; i <= s; ++i) {
            int lca = get_lca(cities[i], cities[i + 1]);

            update(1, 1, n, in[cities[i]], +1);
            update(1, 1, n, in[cities[i + 1]], +1);
            update(1, 1, n, in[lca], -2);
        }
    }


    vector<int> ans;

    for (int i = 1; i <= n; ++i) {
        if (query(1, 1, n, in[i], out[i]) >= 2 * k) {
            ans.push_back(parentEdgeIndex[i]);
        }
    }

    sort(ans.begin(), ans.end());

    cout << ans.size() << endl;

    for (int i = 0; i < ans.size(); ++i) cout << ans[i] << " ";
    cout << endl;

    return 0;
}

Compilation message (stderr)

railway.cpp: In function 'int main()':
railway.cpp:159:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  159 |     for (int i = 0; i < ans.size(); ++i) cout << ans[i] << " ";
      |                     ~~^~~~~~~~~~~~

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