Submission #25877

#	Time	Username	Problem	Language	Result	Execution time	Memory
25877		nibnalin	Network (BOI15_net)	C++14	100 / 100	723 ms	42512 KiB

net

#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
using namespace std;

const int maxn = int(5e5)+5;

vector<int> graph[maxn], S;

void dfs(int node, int par)
{
	if(int(graph[node].size()) == 1) S.push_back(node);
	for(auto it: graph[node])
	{
		if(it != par) dfs(it, node);
	}
}

int main(void)
{
	int n, u, v;
	scanf("%d", &n);
	for(int i = 1;i < n;i++)
	{
		scanf("%d%d", &u, &v);
		u--, v--;
		graph[u].push_back(v), graph[v].push_back(u);
	}

	dfs(0, -1);

	int res = ceil(int(S.size())/2.0);
	printf("%d\n", res);
	for(int i = 0;i < res;i++)
	{
		printf("%d %d\n", S[i]+1, S[(res+i)%int(S.size())]+1);
	}
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:23:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
                 ^
net.cpp:26:24: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &u, &v);
                        ^

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