Submission #849148

#	Time	Username	Problem	Language	Result	Execution time	Memory
849148		sandry24	Network (BOI15_net)	C++17	100 / 100	362 ms	47716 KiB

net

#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pi;
#define pb push_back
#define mp make_pair
#define f first
#define s second

vector<vi> adj(500005);
vi leaves;

void dfs(int x, int p){
    bool has_children = 0;
    for(auto i : adj[x]){
        if(i != p){
            dfs(i, x);
            has_children = 1;
        }
    }
    if(!has_children)
        leaves.pb(x);
}
 
void solve(){
    int n;
    cin >> n;
    for(int i = 0; i < n-1; i++){
        int a, b;
        cin >> a >> b;
        adj[a].pb(b);
        adj[b].pb(a);
    }
    if(adj[1].size() == 1)
        leaves.pb(1);
    dfs(1, -1);
    cout << ceil((double)leaves.size()/2) << '\n';
    for(int i = 0; i < leaves.size()/2; i++)
        cout << leaves[i] << ' ' << leaves[i + leaves.size()/2] << '\n';
    if(leaves.size() & 1)
        cout << leaves[0] << ' ' << leaves.back() << '\n';
}
 
int main(){
    //freopen("flota.in", "r", stdin);
    //freopen("flota.out", "w", stdout);
    ios::sync_with_stdio(0); cin.tie(0);
    int t = 1;
    //cin >> t;
    while(t--){
        solve();
    }
}

Compilation message (stderr)

net.cpp: In function 'void solve()':
net.cpp:40:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   40 |     for(int i = 0; i < leaves.size()/2; i++)
      |                    ~~^~~~~~~~~~~~~~~~~

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