Submission #42248

#	Time	Username	Problem	Language	Result	Execution time	Memory
42248		5ak0	Network (BOI15_net)	C++14	0 / 100	14 ms	12772 KiB

net

/*
ID: 5ak0
PROG:
LANG: C++11
*/

#include <bits/stdc++.h>
#define fr first
#define sc second
#define pb push_back
#define mpr make_pair

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
const int INF = 1e9 + 7, MAXN =500010;

bool u[MAXN];
vector <int> g[MAXN], vec;
queue <pii> q;
int n, a, b;

void dfs(int v){
    u[v] = 1;
    bool ok = 1;
    for (auto to : g[v]){
        if (u[to] == 0){
            ok = 0;
            dfs(to);
        }
    }
    if (ok == 1)
        vec.pb(v);
}

int main(){
    ios_base::sync_with_stdio(0);
    #ifndef SAKO
    //freopen(".in", "r", stdin);
    //freopen(".out", "w", stdout);
    #endif // SAKO

    cin >> n;
    for (int i = 1; i < n; ++i){
        cin >> a >> b;
        g[a].pb(b);
        g[b].pb(a);
    }
    int root = 1;
    while (root <= n && g[root].size() == 1)
        ++root;
    dfs(root);
    memset(u, 0, sizeof(u));
    for (int i = 0; i < vec.size(); ++i){
        if (u[vec[i]] == 0){
            if (i + 1 < vec.size())
                q.push({vec[i], vec[i + 1]}), u[vec[i + 1]] = 1;
            else{
                if (0 < i - 1)
                    q.push({vec[i], vec[i - 1]}), u[vec[i]] = 1, u[vec[i - 1]] = 1;
                else
                    q.push({vec[i], root}), u[vec[i]] = 1;
            }
        }
    }
    cout << q.size() << "\n";
    while (!q.empty()){
        cout << q.front().fr << " " << q.front().sc << "\n";
        q.pop();
    }
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:55:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < vec.size(); ++i){
                       ^
net.cpp:57:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (i + 1 < vec.size())
                       ^

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37