제출 #747506

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
747506		vjudge1	Railway (BOI17_railway)	C++17	0 / 100	95 ms	23436 KiB

railway

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

using namespace std;

const int MAXN = 100001;
const int K = 20;

int n, m, k, x;
vector<pair<int, int>> g[MAXN];
int cnt[MAXN], up[MAXN][K], d[MAXN], deg[MAXN];

void dfs(int u, int p = 0) {
    d[u] = d[p] + 1;
    up[u][0] = p;
    for (int i = 1; i < K; i++) {
        up[u][i] = up[up[u][i - 1]][i - 1];
    }
    for (auto v : g[u]) {
        if (v.first != p) {
            dfs(v.first, u);
        }
    }
    
}

int lca(int a, int b) {
    int i = 19;
    if (d[a] < d[b])swap(a, b);
    while (i >= 0 && d[a] > d[b]) {
        if (d[up[a][i]] >= d[b])a = up[a][i];
        i--;
    }
    if (a == b)return a;
    for (i = 19; i >= 0; i--) {
        if (up[a][i] != up[b][i]) {
            a = up[a][i];
            b = up[b][i];
        }
    }
    return up[a][0];
}

vector<int> ans;
int dfs2(int x, int p, int id) {
    for (auto u : g[x]) {
        if (u.first != p) cnt[x] += dfs2(u.first, x, u.second);
    }
    if (cnt[x] >= k && id)ans.push_back(id);
    return cnt[x];
}

int main()
{
    ios::sync_with_stdio(0); cin.tie(0);
    cin >> n >> m >> k;
    
    for (int i = 1; i <= n - 1; i++) {
        int a, b; cin >> a >> b;
        g[a].push_back({ b,i });
        g[b].push_back({ a,i });
        deg[a]++;
        deg[b]++;

    }
    int st;
    for (int i = 1; i <= n; i++) {
        if (deg[i] < 2) {
            st = i;
            dfs(i);
            break;
        }
    }
    for (int i = 1; i <= m; i++) {
        cin >> x;
        vector<int> v(x);
        for (int& i : v)cin >> i;
        sort(v.begin(), v.end(), [](int a, int b) {return d[a] < d[b]; });
        int a=v[0], b=v.back(), u = lca(a, b);
        cnt[u] -= 2;
        cnt[a]++;
        cnt[b]++;
    }
    dfs2(st, 0, 0);
    cout << ans.size() << '\n';
    for (int i : ans)cout << i << ' ';
    cout << endl;
    return 0;
}

컴파일 시 표준 에러 (stderr) 메시지

railway.cpp: In function 'int main()':
railway.cpp:85:9: warning: 'st' may be used uninitialized in this function [-Wmaybe-uninitialized]
   85 |     dfs2(st, 0, 0);
      |     ~~~~^~~~~~~~~~

• Subtask 1: 0 / 8
• Subtask 2: 0 / 15
• Subtask 3: 0 / 7
• Subtask 4: 0 / 29
• Subtask 5: 0 / 16
• Subtask 6: 0 / 25