Submission #828291

#	Time	Username	Problem	Language	Result	Execution time	Memory
828291		vjudge1	Network (BOI15_net)	C++14	100 / 100	366 ms	60220 KiB

net

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

#define ll long long
#define vi vector<ll>
#define pi pair<ll,ll>
#define fi first
#define se second
#define gcd __gcd
#define mset(a,v) memset(a, v, sizeof(a))
#define endl '\n'

const int N = 1e6 + 5,LOG = 27;
const ll MOD = 1e9 + 7,INF = 1e9;
ll n; vector<ll>g[N];
vector<ll>leaf; bool vis[N];
void dfs(ll u,ll p = 0){
    if(g[u].size() == 1)leaf.push_back(u);
    for(ll &v : g[u])
        if(v != p) dfs(v,u); 
}
void solve(){
    cin>>n;
    for(ll i = 1;i < n;++i){
        ll u,v; cin>>u>>v; 
        g[u].push_back(v);
        g[v].push_back(u);
    }
    dfs(1);
    cout<<(leaf.size() + 1)/2<<endl;
    for(ll i = 0;2*i < leaf.size();++i)
        cout<<leaf[i]<<" "<<leaf[i + leaf.size()/2]<<endl;
}

signed main(){
    cin.tie(0); cout.tie(0); 
    ios_base::sync_with_stdio(false);
    ll t = 1; //cin>>t;
    while(t--) solve(); 
    cerr << endl << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
}

Compilation message (stderr)

net.cpp: In function 'void solve()':
net.cpp:31:22: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   31 |     for(ll i = 0;2*i < leaf.size();++i)
      |                  ~~~~^~~~~~~~~~~~~

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