Submission #1213428

#	Time	Username	Problem	Language	Result	Execution time	Memory
1213428		minhpk	Network (BOI15_net)	C++20	0 / 100	13 ms	23872 KiB

net

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

int a;
vector<int> z[1000005];
vector<int> v;
int sta[1000005];
int tour;

void dfs(int i, int parent) {
    sta[i] = ++tour;
    for (auto p : z[i]) {
        if (p == parent) continue;
        dfs(p, i);
    }
}

bool cmp(int A, int B) {
    return sta[A] < sta[B];
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    cin >> a;
    for (int i = 1; i < a; i++) {
        int x, y;
        cin >> x >> y;
        z[x].push_back(y);
        z[y].push_back(x);
    }

    for (int i = 1; i <= a; i++) {
        if (z[i].size() == 1) {
            v.push_back(i);
        }
    }

    dfs(1, 0);

    int k = v.size();
    cout << (k + 1) / 2 << "\n";

    sort(v.begin(), v.end(), cmp);
    if (k % 2 == 1) {
       
        v.push_back(v[0]);
    }
    for (int i = 0; i < v.size(); i += 2) {
        cout << v[i] << " " << v[i + 1] << "\n";
    }

    return 0;
}

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37