Submission #748398

#	Time	Username	Problem	Language	Result	Execution time	Memory
748398		mariowong	Network (BOI15_net)	C++14	0 / 100	2 ms	2644 KiB

net

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

int t;
vector <int> edge[100005];
int dis[100005];
bool vis[100005],ok[100005];
void dfs(int x){
	vis[x]=true; t=x;
	for (int i=0;i<edge[x].size();i++){
		if (!vis[edge[x][i]]) dfs(edge[x][i]);
	}
}
void dfs2(int x,int d){
	vis[x]=true; dis[x]=d;
	for (int i=0;i<edge[x].size();i++){
		if (!vis[edge[x][i]]) dfs2(edge[x][i],d+1);
	}
}
void dfs3(int x,int d){
	ok[x]=true;
	for (int i=0;i<edge[x].size();i++){
		if (dis[edge[x][i]] == d-1){
			dfs3(edge[x][i],d-1);
			break;
		}
	}
}
int main(){
	ios::sync_with_stdio(false); 
	int n;
	cin >> n;
	for (int i=1;i<n;i++){
		int u,v;
		cin >> u >> v;
		edge[u].push_back(v);
		edge[v].push_back(u);
	}	
	dfs(1);
	for (int i=1;i<=n;i++) vis[i]=false;
	dfs2(t,0);
	int node=1;
	for (int i=1;i<=n;i++){
		if (dis[i] > dis[node]) node=i;
	}
	dfs3(node,dis[node]);
	cout << n-dis[node]-1 << "\n";
	for (int i=1;i<=n;i++){
		if (!ok[i]){
			cout << node << " " << i << "\n";
			node=i;
		}
	}
	return 0;
}

Compilation message (stderr)

net.cpp: In function 'void dfs(int)':
net.cpp:10:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |  for (int i=0;i<edge[x].size();i++){
      |               ~^~~~~~~~~~~~~~~
net.cpp: In function 'void dfs2(int, int)':
net.cpp:16:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   16 |  for (int i=0;i<edge[x].size();i++){
      |               ~^~~~~~~~~~~~~~~
net.cpp: In function 'void dfs3(int, int)':
net.cpp:22:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |  for (int i=0;i<edge[x].size();i++){
      |               ~^~~~~~~~~~~~~~~

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