Submission #113191

#	Time	Username	Problem	Language	Result	Execution time	Memory
113191		davitmarg	Network (BOI15_net)	C++17	100 / 100	705 ms	43380 KiB

net

/*DavitMarg*/
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <cstring>
#include <map>
#include <set>
#include <queue>
#include <iomanip>
#include <bitset>
#include <stack>
#include <cassert>
#include <iterator>
#include <ctype.h>
#include <fstream>
#define mod 1000000007ll
#define LL long long
#define LD long double
#define MP make_pair
#define PB push_back
#define all(v) v.begin (),v.end()
using namespace std;

int n,used[500005],start;
vector<int> g[500005],t;
vector<pair<int, int>> ans;

void dfs(int v, int d = 0)
{
	used[v] = 1;
	for (int i = 0; i < g[v].size(); i++)
	{
		int to = g[v][i];
		if (used[to])
			continue;
		if (g[to].size() == 1)
			t.PB(to);
	}
	for (int i = 0; i < g[v].size(); i++)
	{
		int to = g[v][i];
		if (used[to] || g[to].size() == 1)
			continue;
		dfs(to,d+1);
	}
}

int main()
{
	cin >> n;
	if (n == 0)
	{
		printf("0\n");
		return 0;
	}
	else if (n == 2)
	{
		printf("1\n");
		printf("1 2\n");
		return 0;
	}
	for (int i = 1; i < n; i++)
	{
		int a, b;
		scanf("%d%d", &a, &b);
		g[a].PB(b);
		g[b].PB(a);
	}
	for(int i=1;i<=n;i++)
		if (g[i].size() != 1)
		{
			start = i;
			break;
		}
	dfs(start);

	for (int i = 0; i + t.size() / 2 < t.size(); i++)
		ans.PB(MP(t[i], t[i+ t.size() / 2]));


	printf("%d\n",(int)ans.size());
	for (int i = 0; i < ans.size(); i++)
		printf("%d %d\n", ans[i].first, ans[i].second);

	return 0;
}

/*



*/

Compilation message (stderr)

net.cpp: In function 'void dfs(int, int)':
net.cpp:33:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < g[v].size(); i++)
                  ~~^~~~~~~~~~~~~
net.cpp:41:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < g[v].size(); i++)
                  ~~^~~~~~~~~~~~~
net.cpp: In function 'int main()':
net.cpp:84:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < ans.size(); i++)
                  ~~^~~~~~~~~~~~
net.cpp:67:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &a, &b);
   ~~~~~^~~~~~~~~~~~~~~~

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