Submission #1084613

#	Time	Username	Problem	Language	Result	Execution time	Memory
1084613		_rain_	Network (BOI15_net)	C++14	100 / 100	201 ms	47824 KiB

net

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

#define fixbug true

const int maxn = 5e5;
vector<int> g[maxn+2];
vector<int> leaf;
int n;

void dfs(int u , int p){
    if (g[u].size()==1) leaf.push_back(u);
    for (auto& v : g[u]){
        if (v != p) dfs(v,u);
    }
    return;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    #define name "main"
    if (fopen(name".inp","r")){
        freopen(name".inp","r",stdin);
    }
    cin >> n;
    for (int i = 1; i < n; ++i){
        int u , v; cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    for (int i = 1; i <= n; ++i){
        if (g[i].size() > 1){
            dfs(i,i);
            break;
        }
    }
    if (leaf.size()%2==1) leaf.push_back(leaf.front());
    cout << leaf.size() / 2 << '\n';
    for (int i = 0; i < leaf.size() / 2; i++){
        cout << leaf[i] << ' ' << leaf[leaf.size()/2 + i] << '\n';
    }
    exit(0);
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:41:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   41 |     for (int i = 0; i < leaf.size() / 2; i++){
      |                     ~~^~~~~~~~~~~~~~~~~
net.cpp:25:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   25 |         freopen(name".inp","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

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