Submission #1270383

#	Time	Username	Problem	Language	Result	Execution time	Memory
1270383		vuquangsang	Railway (BOI17_railway)	C++20	100 / 100	77 ms	27584 KiB

railway

#include <bits/stdc++.h>
using namespace std;

#define     el "\n"
#define     FOR(i,a,b) for(int i = (a), _b = (b); i <= _b; i++)
#define     FORD(i,a,b) for(int i = (a), _b = (b); i >= _b; i--)
#define     pb push_back
#define     fi first
#define     se second
#define     all(x) x.begin(),x.end()
#define     lg(x) __lg(x)
#define     alla(a,n) a+1,a+n+1
#define     ll long long


template <class T> bool maxi(T &x, T y) { if(x < y) { x = y ; return true ;} return false;}
template <class T> bool mini(T &x, T y) { if(x > y) { x = y ; return true ;} return false;}


const int N = 1e5 + 2;

int n, q, k;
vector<pair<int, int>> adj[N];
void inp()
{
    cin >> n >> q >> k;
    FOR(i, 1, n - 1) {
        int x, y; cin >> x >> y;
        adj[x].pb({y, i});
        adj[y].pb({x, i});
    }
}

/* Try your best
    No regrets */

namespace subtask_1
{
    int h[N], up[N][21];
    int in[N], out[N], time = 0;

    int ID[N];
    void dfs(int u, int p)
    {
        in[u] = ++time;

        up[u][0] = p;
        FOR(j, 1, lg(n)) up[u][j] = up[up[u][j - 1]][j - 1];
        for(pair<int, int> x : adj[u]) {
            int v = x.first, id = x.second;
            if(v == p) continue;
            ID[v] = id;
            h[v] = h[u] + 1;
            dfs(v, u);
        }
        out[u] = time;
    }
    int LCA(int u, int v)
    {
        if(h[u] < h[v]) swap(u, v);
        FORD(j, lg(n), 0) if(h[up[u][j]] >= h[v]) u = up[u][j];
        if(u == v) return u;
        FORD(j, lg(n), 0) if(up[u][j] != up[v][j]) {
            u = up[u][j];
            v = up[v][j];
        }
        return up[u][0];
    }

    vector<int> g[N];

    int Val[N];
    void update(int u, int v)
    {
        int p = LCA(u, v);
        Val[u]++;
        Val[v]++;
        Val[p] -= 2;

    }
    void dfs_pre(int u, int p)
    {
        for(int v : g[u]) if(v != p) {
            update(u, v);
            dfs_pre(v, u);
        }
    }
    void dfsAns(int u, int p)
    {
        for(pair<int, int> x : adj[u]) {
            int v = x.first, id = x.second;
            if(v == p) continue;
            dfsAns(v, u);
            Val[u] += Val[v];
        }
    }
    void slv()
    {
        dfs(1, 1);
        FOR(qry, 1, q) {
            int x; cin >> x;
            vector<int> V;
            FOR(i, 1, x) {
                int v; cin >> v;
                V.pb(v);
            }
            sort(all(V),[](int x, int y){
                return in[x] < in[y];
            });

            int sz = V.size();
            for(int i = 0; i < sz - 1; i++) {
                V.pb(LCA(V[i], V[i + 1]));
            }
            sort(all(V),[](int x, int y){
                return in[x] < in[y];
            });
            V.resize(unique(all(V)) - V.begin());

            deque<int> dq;

            for(int v : V) g[v].clear();

//            cout << "Queries " << qry << el;
            for(int v : V) {
                while(!dq.empty() && out[dq.back()] < in[v]) dq.pop_back();
                if(dq.size()) {
//                    cout << dq.back() << " " << v << el;
                    g[dq.back()].pb(v);
                    g[v].pb(dq.back());
                }

                dq.push_back(v);
            }

            dfs_pre(V[0], 0);

        }
        dfsAns(1, 0);

        int ans = 0;

        vector<int> isAns;

        FOR(i, 2, n) if(Val[i] >= k) {
            isAns.pb(ID[i]);
        }
        sort(all(isAns));
        cout << isAns.size() << el;
        for(int x : isAns) cout << x << " ";
    }
}

/* Code slowly, think carefully */

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

    #define __Azul__ "task"
    if(fopen(__Azul__".inp", "r")) {
        freopen(__Azul__".inp", "r", stdin);
        freopen(__Azul__".out", "w", stdout);
    }

    bool qs = 0;

    int T = 1;
    if(qs) cin >> T;
    while(T--) {
        inp();
        subtask_1::slv();
    }

    cerr << "\nTime" << 0.001 * clock() << "s "; return 0;


}

Compilation message (stderr)

railway.cpp:156:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
  156 | main()
      | ^~~~
railway.cpp: In function 'int main()':
railway.cpp:162:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  162 |         freopen(__Azul__".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
railway.cpp:163:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  163 |         freopen(__Azul__".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