Submission #996727

#	Time	Username	Problem	Language	Result	Execution time	Memory
996727		juliany2	Mergers (JOI19_mergers)	C++17	100 / 100	643 ms	110804 KiB

mergers

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(x) (x).begin(), (x).end()
 
const int N = 5e5 + 7, L = 20;
int n, k;
vector<int> adj[N];
int c[N], dep[N];
int lift[N][L];
int l[N], cum[N];
int cnt, r;
bool seen[N];
 
void prep(int v = 1, int p = 0) {
    lift[v][0] = p;
    for (int i = 1; i < L; i++)
        lift[v][i] = lift[lift[v][i - 1]][i - 1];
 
    for (int u : adj[v]) {
        if (u == p)
            continue;
 
        dep[u] = dep[v] + 1;
        prep(u, v);
    }
}
 
int lca(int u, int v) {
    if (u == 0 || v == 0)
        return max(u, v);
 
    if (dep[u] > dep[v])
        swap(u, v);
 
    for (int i = 0; i < L; i++)
        if ((dep[v] - dep[u]) >> i & 1)
            v = lift[v][i];
 
    if (u == v)
        return u;
 
    for (int i = L - 1; i >= 0; i--)
        if (lift[v][i] != lift[u][i])
            v = lift[v][i], u = lift[u][i];
 
    return lift[u][0];
}
 
void run(int v = 1, int p = 0) {
    for (int u : adj[v]) {
        if (u == p)
            continue;
 
        run(u, v);
        cum[v] += cum[u];
    }
}
 
void dfs(int v = 1, int p = 0) {
    for (int u : adj[v]) {
        if (u == p)
            continue;
 
        dfs(u, v);
        seen[v] |= seen[u];
    }
 
    if (v != 1 && !cum[v] && !seen[v]) {
        cnt++;
        r = lca(r, v);
        seen[v] = 1;
    }
}
 
int main() {
    cin.tie(0)->sync_with_stdio(false);
 
    cin >> n >> k;
 
    for (int i = 1; i < n; i++) {
        int u, v;
        cin >> u >> v;
 
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
 
    prep();
 
    for (int i = 1; i <= n; i++) {
        cin >> c[i];
 
        l[c[i]] = lca(l[c[i]], i);
    }
 
    for (int i = 1; i <= n; i++)
        cum[i]++, cum[l[c[i]]]--;
 
    run();
 
    dfs();
 
    if (!r) {
        cout << 0 << '\n';
        return 0;
    }
 
    int need = 0;
    while (r != 1) {
        if (!cum[r])
            need = 1;
 
        r = lift[r][0];
    }
 
    cout << ((cnt | need) + 1) / 2 << '\n';
 
    return 0;
}

• Subtask 1: 10 / 10
• Subtask 2: 24 / 24
• Subtask 3: 14 / 14
• Subtask 4: 22 / 22
• Subtask 5: 30 / 30