Submission #606591

#	Time	Username	Problem	Language	Result	Execution time	Memory
606591		nguyentunglam	Network (BOI15_net)	C++14	100 / 100	498 ms	68212 KiB

net

#include<bits/stdc++.h>
#define forin(i, a, b) for(int i = a; i <= b; i++)
#define forde(i, a, b) for(int i = a; i >= b; i--)
#define forv(a, b) for(auto & a : b)
#define fi first
#define se second
using namespace std;
const int N = 5e5 + 10;
int n;
vector<int> adj[N];
vector<pair<int, int>> ans;
vector<int> dfs(int u, int par) {
    vector<int> f;
    if (adj[u].size() == 1) {
        f.push_back(u);
        return f;
    }
    forv(v, adj[u]) if (v != par) {
        vector<int> g = dfs(v, u);
        if (f.size() < g.size()) swap(f, g);
        while (f.size() + g.size() > 2) {
            ans.push_back({f.back(), g.back()});
            f.pop_back(); g.pop_back();
        }
        forv(t, g) f.push_back(t);
    }
    return f;
}
int main() {
    cin.tie(0) -> sync_with_stdio(0);
    if (fopen ("task.inp", "r")) {
        freopen ("task.inp", "r", stdin);
        freopen ("task.out", "w", stdout);
    }
    if (fopen ("bluehouse.inp", "r")) {
        freopen ("bluehouse.inp", "r", stdin);
        freopen ("bluehouse.out", "w", stdout);
    }
    cin >> n;
    forin(i, 1, n - 1) {
        int a, b; cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    forin(i, 1, n) if (adj[i].size() > 1) {
        vector<int> t = dfs(i, 0);
        if (t.size() >= 2) {
            int u = t.back(); t.pop_back();
            int v = t.back(); t.pop_back();
            ans.push_back({u, v});
        }
        if (!t.empty()) ans.push_back({i, t[0]});
        break;
    }
    cout << ans.size() << "\n";
    forv(v, ans) cout << v.fi << " " << v.se << "\n";
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:32:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   32 |         freopen ("task.inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:33:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   33 |         freopen ("task.out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:36:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |         freopen ("bluehouse.inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:37:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |         freopen ("bluehouse.out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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