oj.uz

Submission #656117

# Submission time Handle Problem Language Result Execution time Memory
656117 2022-11-06T10:12:18 Z Kahou Network (BOI15_net) C++14
0 / 100
 3 ms 4948 KB 
#include<bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define endl '\n'
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int N = 1e5 + 50;
int n, sub[N], k, par[N], t;
vector<int> adj[N];
vector<int> vc[N];
set<pii> st;
vector<pii> out;

void dfs(int u, int p) {
        par[u] = p;
        for (int v:adj[u]) {
                if (v == p) continue;
                dfs(v, u);
                sub[u] += sub[v];
        }
}

void dfs2(int u, int p) {
        if (adj[u].size() == 1) {
                vc[t].push_back(u);
        }
        for (int v:adj[u]) {
                if (v == p) continue;
                dfs2(v, u);
        }
}

void solve() {
        cin >> n;
        for (int i = 1; i <= n-1; i++) {
                int u, v;
                cin >> u >> v;
                adj[u].push_back(v);
                adj[v].push_back(u);
        }
        for (int u = 1; u <= n; u++) {
                if (adj[u].size() == 1) {
                        k++;
                        sub[u] = 1;
                }
        }
        dfs(1, 0);
        int r = 0;
        for (int u = 1; u <= n; u++) {
                bool flg = 1;
                for (int v:adj[u]) {
                        if (v == par[u]) flg = flg&&(k-sub[u] <= k/2);
                        else flg = flg&&(sub[v] <= k/2);
                }
                if (adj[u].size() > 1 && flg) {
                        r = u;
                        break;
                }
        }
        for (int u:adj[r]) {
                t++;
                dfs2(u, r);
        }
        for (int i = 1; i <= t; i++) {
                st.insert({-vc[i].size(), i});
        }
        while (st.size() >= 2) {
                int A = st.begin()->S;
                int B = next(st.begin())->S;

                out.push_back({vc[A].back(), vc[B].back()});
                st.erase({-vc[A].size(), A});
                st.erase({-vc[B].size(), B});
                vc[A].pop_back();
                vc[B].pop_back();
                if (vc[A].size()) st.insert({-vc[A].size(), A});
                if (vc[B].size()) st.insert({-vc[B].size(), B});
        }
        if (st.size()) {
                int A = st.begin()->S;
                int u = vc[A].back();
                out.push_back({u, adj[u][0]});
                st.erase(st.begin());
        }
        cout << out.size() << endl;
        for (pii x:out) {
                cout << x.F << ' ' << x.S << endl;
        }
}

int main() {
        ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
        solve();
        return 0;
}

Subtask #1
0 / 18.0

# Verdict Execution time Memory Grader output
1 Correct 2 ms 4948 KB Output is correct
2 Correct 2 ms 4948 KB Output is correct
3 Correct 2 ms 4948 KB Output is correct
4 Correct 3 ms 4948 KB Output is correct
5 Correct 2 ms 4948 KB Output is correct
6 Correct 3 ms 4948 KB Output is correct
7 Incorrect 3 ms 4948 KB Breaking single line is causing network to disconnect.
8 Halted 0 ms 0 KB -

Subtask #2
0 / 45.0

# Verdict Execution time Memory Grader output
1 Correct 2 ms 4948 KB Output is correct
2 Correct 2 ms 4948 KB Output is correct
3 Correct 2 ms 4948 KB Output is correct
4 Correct 3 ms 4948 KB Output is correct
5 Correct 2 ms 4948 KB Output is correct
6 Correct 3 ms 4948 KB Output is correct
7 Incorrect 3 ms 4948 KB Breaking single line is causing network to disconnect.
8 Halted 0 ms 0 KB -

Subtask #3
0 / 37.0

# Verdict Execution time Memory Grader output
1 Correct 2 ms 4948 KB Output is correct
2 Correct 2 ms 4948 KB Output is correct
3 Correct 2 ms 4948 KB Output is correct
4 Correct 3 ms 4948 KB Output is correct
5 Correct 2 ms 4948 KB Output is correct
6 Correct 3 ms 4948 KB Output is correct
7 Incorrect 3 ms 4948 KB Breaking single line is causing network to disconnect.
8 Halted 0 ms 0 KB -