Submission #291584

#	Time	Username	Problem	Language	Result	Execution time	Memory
291584		Fischer	Network (BOI15_net)	C++14	0 / 100	9 ms	12032 KiB

net

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

const int maxn = 5e5 + 10;
vector<int> g[maxn];
int n;
using ii = pair<int, int>;

int dfs(vector<ii>& edges, int x, int p=0) {
    int node = g[x].size() == 1 ? x : -1;
    for (int v : g[x]) {
        if (v==p) continue;
        int u = dfs(edges, v, x);
        if (node == -1) node = u;
        else if (u != -1) edges.emplace_back(node, u), node = -1;
    }
    return node;
}

int main() {
    scanf("%d", &n);
    for (int i=0; i<n-1; ++i) {
        int a, b;
        scanf("%d%d", &a, &b);
        g[a].emplace_back(b);
        g[b].emplace_back(a);
    }
    vector<ii> edges;
    for (int i=1; i<=n; ++i) {
        if (g[i].size()>1) {
            int extra = dfs(edges, i);
            if (extra != -1) edges.emplace_back(extra, i);
            break;
        }
    }
    cout << edges.size() << endl;
    for (auto e : edges) cout << e.first << " " << e.second << '\n';
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:21:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   21 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
net.cpp:24:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   24 |         scanf("%d%d", &a, &b);
      |         ~~~~~^~~~~~~~~~~~~~~~

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