Submission #482462

#	Time	Username	Problem	Language	Result	Execution time	Memory
482462		Saacoota	Network (BOI15_net)	C++14	18 / 100	8 ms	12068 KiB

net

#include <bits/stdc++.h>

using namespace std;

const int maxn = 5e5 + 10;

vector < int > g[maxn] , leaf;
int cnt[maxn] , par[maxn];

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

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    int n , root;
    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);
        if (g[u].size() > 1) root = u;
        if (g[v].size() > 1) root = v;
    }
    DFS(root , 0);
    int half = leaf.size() / 2;
    cout << (leaf.size() + 1) / 2 << '\n';
    if ((leaf.size()) % 2 == 0) {
        for (int j = 0 ; j < half ; ++j)
        cout << leaf[j] << ' ' << leaf[half + j] << '\n';
    } else {
        int ma = 0;
        for (auto v : leaf) {
            cnt[par[v]]++;
            ma = max(ma , cnt[par[v]]);
        }
        int pos;
        for (int i = 0 ; i < leaf.size() ; ++i)
        if (cnt[par[leaf[i]]] == ma) {
            cout << leaf[i] << ' ' << root << '\n';
            pos = i;
            break;
        }
        leaf.erase(leaf.begin() + pos);
        for (int j = 0 ; j < half ; ++j)
        cout << leaf[j] << ' ' << leaf[half + j] << '\n';
    }
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:45:28: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   45 |         for (int i = 0 ; i < leaf.size() ; ++i)
      |                          ~~^~~~~~~~~~~~~
net.cpp:47:47: warning: 'root' may be used uninitialized in this function [-Wmaybe-uninitialized]
   47 |             cout << leaf[i] << ' ' << root << '\n';
      |                                               ^~~~

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