Submission #716752

#	Time	Username	Problem	Language	Result	Execution time	Memory
716752		Spade1	Network (BOI15_net)	C++14	100 / 100	430 ms	50040 KiB

net

#pragma GCC optimize("O3")
#include<bits/stdc++.h>
//#include <grader.h>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define ll long long
#define ld long double
#define st first
#define nd second
#define pb push_back
#define INF INT_MAX
#define db double
using namespace std;

const int N = 5e5 + 10;

vector<int> v;
vector<int> adj[N];

void dfs(int i, int prt) {
    for (auto j : adj[i]) if (j != prt) dfs(j, i);
    if (adj[i].size() == 1) v.pb(i);
}

void solve() {
    int n; cin >> n;
    for (int i = 1; i < n; ++i) {
        int u, v; cin >> u >> v;
        adj[u].pb(v); adj[v].pb(u);
    }
    int root;
    for (int i = 1; i <= n; ++i) if (adj[i].size() > 1) root = i;
    dfs(root, 0);
    int sz = v.size();
    cout << (sz+1)/2 << '\n';
    for (int i = 0; i < sz/2; ++i) {
        cout << v[i] << " " << v[i+sz/2] << '\n';
    }
    if (sz&1) cout << v[sz-1] << " " << v[0] << '\n';
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(NULL);
    int t = 1;
//    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'void solve()':
net.cpp:31:9: warning: 'root' may be used uninitialized in this function [-Wmaybe-uninitialized]
   31 |     int root;
      |         ^~~~

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