Submission #443499

#	Time	Username	Problem	Language	Result	Execution time	Memory
443499		BeanZ	Network (BOI15_net)	C++14	100 / 100	538 ms	64448 KiB

net

// I_Love_LPL 1y0m2d
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
const int N = 1e6 + 5;
long long mod = 1000007;
const int lim = 4e5 + 5;
const int lg = 20;
const int base = 311;
const long double eps = 1e-6;
vector<ll> node[N];
vector<ll> one;
void dfs(ll u, ll p){
    for (auto j : node[u]){
        if (j == p) continue;
        dfs(j, u);
    }
    if (node[u].size() == 1) one.push_back(u);
}
int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    if (fopen("tests.inp", "r")){
        freopen("test.inp", "r", stdin);
        freopen("test.out", "w", stdout);
    }
    ll n;
    cin >> n;
    for (int i = 1; i < n; i++){
        ll u, v;
        cin >> u >> v;
        node[u].push_back(v);
        node[v].push_back(u);
    }
    for (int i = 1; i <= n; i++){
        if (node[i].size() != 1){
            dfs(i, i);
            break;
        }
    }
    cout << (one.size() + 1) / 2 << endl;
    for (int i = 0; i < (one.size() + 1) / 2; i++){
        cout << one[i] << " " << one[i + one.size() / 2] << endl;
    }
}
/*
Ans:

Out:
*/

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:43:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   43 |     for (int i = 0; i < (one.size() + 1) / 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("test.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:26:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   26 |         freopen("test.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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