Submission #119011

#	Time	Username	Problem	Language	Result	Execution time	Memory
119011		SOIVIEONE	Network (BOI15_net)	C++14	0 / 100	19 ms	12672 KiB

net

#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>

#define INF 1000000021
#define MOD 1000000007
#define pb push_back
#define sqr(a) (a)*(a)
#define M(a, b) make_pair(a,b)
#define T(a, b, c) make_pair(a, make_pair(b, c))
#define F first
#define S second
#define all(x) (x.begin(), x.end())
#define deb(x) cerr << #x << " = " << x << '\n'
#define N 522222

using namespace std;
//using namespace __gnu_pbds;

typedef long double ld;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
//typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> indexed_set;

const ld pi = 2 * acos(0.0);
template<class T> bool umin(T& a, T b){if(a>b){a=b;return 1;}return 0;}
template<class T> bool umax(T& a, T b){if(a<b){a=b;return 1;}return 0;}
template<class T, class TT> bool pal(T a, TT n){int k=0;for(int i=0;i<=n/2;i++){if(a[i]!=a[n-i-1]){k=1;break;}}return k?0:1;}

//int month[] = {0,31,28,31,30,31,30,31,31,30,31,30,31};

int h[N], l[N];
vi v[N];
void dfs(int u, int e)
{
	h[u] = h[e] + 1;
	for(auto it : v[u])
		if(it != e)
			dfs(it, u);
}

bool kk(int x, int y)
{
	return (h[x] < h[y]);
}

int main()
{
	int n;
	cin >> n;
	for(int i = 2; i <= n; i ++)
	{
		int x, y;
		cin >> x >> y;
		v[x].pb(y);
		v[y].pb(x);
	}
	int mx = 0, root = 0;
	int cnt = 0;
	for(int i = 1; i <= n ;i ++)
	{
		if(mx < v[i].size())
		{
			mx = v[i].size();
			root = i;
		}
		if(v[i].size() == 1)
			l[++cnt] = i;
	}
	dfs(root, 0);
//	deb(root);
	sort(l + 1, l + cnt + 1, kk);
	vector<pii> ans;
	for(int i = 1; i <= cnt/2; i ++)
	{
		ans.pb(M(l[i], l[cnt-i+1]));
	}
	if(cnt & 1)
		ans.pb(M(l[cnt/2+1], l[1]));
	cout << ans.size() << '\n';
	for(auto it : ans)
		cout << it.F << ' ' << it.S << '\n';


	





	getchar();
	getchar();
	return 0;
	//ios::sync_with_stdio(false);
	//cin.tie(0);
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:64:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(mx < v[i].size())
      ~~~^~~~~~~~~~~~~

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