Submission #1268104

#	Time	Username	Problem	Language	Result	Execution time	Memory
1268104		hoa208	Railway (BOI17_railway)	C++20	100 / 100	67 ms	37828 KiB

railway

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; i++)
#define FORD(i, b, a) for (int i = (b), _a = (a); i >= _a; i--)
#define pa pair<ll, ll>
#define fi first
#define se second
#define bit(mask, j) ((mask >> j) & 1)
const   ll mod = 1e9 + 7;
const   ll INF = 1e18;
//--------------------------------------------------------------------
const ll N = 1e5 + 10;
ll st[N];
vector<ll> g[N];
ll timer;
ll n, m, k;
ll h[N], up[N][18];
void dfs(ll u, ll p) {
    st[u] = ++timer;
    for(auto v : g[u]) {
        if(v == p) continue;
        h[v] = h[u] + 1;
        up[v][0] = u;
        FOR(i, 1, 17) {
            up[v][i] = up[up[v][i - 1]][i - 1];
        }
        dfs(v, u);
    }
}
ll get(ll u, ll k) {
    for(int j = 0; (1 << j) <= k; j++) {
        if(bit(k, j)) u = up[u][j];
    }
    return u;
}
ll lca(ll u, ll v) {
    if(h[u] < h[v]) swap(u, v);
    u = get(u, h[u] - h[v]);
    if(u == v) return u;
    FORD(i, 17, 0) {
        if(up[u][i] != up[v][i]) {
            u = up[u][i];
            v = up[v][i];
        }
    }
    return up[u][0];
}
ll f[N];
vector<pa> g2[N];
ll b[N];
void dfs2(ll u, ll p) {
    for(auto e : g2[u]) {
        ll v = e.fi, id = e.se;
        if(v == p) continue;
        b[v] = id;
        dfs2(v, u);
        f[u] += f[v];
    }
}
void hbmt() {
    cin >> n >> m >> k;
    FOR(i, 1, n - 1) {
        ll u, v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
        g2[u].push_back({v, i});
        g2[v].push_back({u, i});
    }
    dfs(1, 0);
    FOR(i, 1, m) {
        ll s;
        cin >> s;
        vector<pa> vt;
        FOR(j, 1, s) {
            ll x;
            cin >> x;
            vt.push_back({st[x], x});
        }
        sort(vt.begin(), vt.end());
        FOR(i, 0, vt.size() - 1) {
            ll u = vt[i].se, v = vt[(i + 1) % vt.size()].se;
            // cout << u << ' ' << v << ' ' << lca(u, v) << '\n';
            f[lca(u, v)] += -2;
            f[u] += 1;
            f[v] += 1;
        }
    }
    dfs2(1, 0);
    vector<ll> vt;
    FOR(i, 2, n) {
        if(f[i] >= 2 * k) {
            vt.push_back(b[i]);
        }
    }
    sort(vt.begin(), vt.end());
    cout << vt.size() << '\n';
    for(auto e : vt) {
        cout << e << ' ';
    }
}

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

    #define NAME "hbmt"
    if(fopen(NAME".inp", "r")) {
        freopen(NAME".inp", "r", stdin);
        freopen(NAME".out", "w", stdout);
    }
    
    //int t;cin>>t;while(t--)
    hbmt();
    return 0;
}

Compilation message (stderr)

railway.cpp: In function 'int main()':
railway.cpp:111:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  111 |         freopen(NAME".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
railway.cpp:112:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  112 |         freopen(NAME".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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