Submission #1117766

#	Time	Username	Problem	Language	Result	Execution time	Memory
1117766		Pwo	Network (BOI15_net)	C++17	0 / 100	3 ms	12880 KiB

net

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

int n, depth[500005], par[500005];
vector<int> g[500005];

void dfs(int v, int p) {
	depth[v] = depth[p] + 1;
	par[v] = p;
	for (const int u : g[v]) {
		if (u != p) dfs(u, v);
	}
}

int32_t main() {
	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);
	}
	
	dfs(1, 1);
	int mx = 0, node = 0;
	for (int i = 1; i <= n; i++) {
		if (depth[i] > mx) mx = depth[i], node = i;
	}
	
	fill(depth, depth + n + 1, 0);
	dfs(node, node);
	mx = 0; int node2 = 0;
	for (int i = 1; i <= n; i++) {
		if (depth[i] > mx) mx = depth[i], node2 = i;
	}
	
	par[node] = -1;
	set<int> st;
	int cur = node2;
	while (cur != -1) {
		st.insert(cur);
		cur = par[cur];
	}
	
	cout << n - mx << '\n';
	for (int i = 1; i <= n; i++) {
		if (st.find(i) == st.end())
			cout << i << ' ' << node << '\n';
	}
}

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