Submission #951416

#	Time	Username	Problem	Language	Result	Execution time	Memory
951416		Doncho_Bonboncho	Network (BOI15_net)	C++14	0 / 100	12 ms	25688 KiB

net

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

template< class T, class T2 > inline bool chkmin( T& a, const T2& b ){ return a > b ? a = b, 1 : 0; }
template< class T, class T2 > inline bool chkmax( T& a, const T2& b ){ return a < b ? a = b, 1 : 0; }

#ifndef LOCAL
#define cerr if( false )cerr
#endif

#define out(x) #x << " = " << x << "  "

typedef long long ll;

const int MAX_N = 1e6 + 42;
const ll mod = 1e9 + 7;

std::vector< int > v[MAX_N];
int par[MAX_N];

void dfs( int x, int p = -1 ){
	par[x] = p;
	for( auto j : v[x] ){
		if( j == p ) continue;
		dfs( j, x );
	}
}
int main (){

#ifndef LOCAL
	std::ios_base::sync_with_stdio( false ); std::cin.tie( NULL ); std::cout.tie( NULL );
#endif

	int n;
	std::cin >> n;

	for( int i=0 ; i < n-1 ; i++ ){
		int a, b;
		std::cin >> a >> b;
		a--; b--;
		v[a].push_back( b );
		v[b].push_back( a );
	}
	
	int st = 0;
	for( int i=0 ; i < n ; i++ ){
		if( v[i].size() == 1){
			st = i;
			break;
		}
	}

	dfs( st );
	std::vector< std::pair< int ,int > > leaves;
	for( int i=0 ; i < n ; i++ ){
		if( v[i].size() == 1 ) leaves.push_back({ par[i], i });
	}

	std::sort( leaves.begin(), leaves.end() );

	ll nas = leaves.size() / 2;
	if( leaves.size() & 1 ){
		nas ++;
		std::cout << nas << endl;
		std::cout << leaves.back().second +1 << " " << leaves[0].second +1 << endl;
		leaves.pop_back();
	}else{
		std::cout << nas << endl;
	}

	for( int i=0 ; i < leaves.size()/ 2 ; i ++ ){
		std::cout << leaves[i].second +1 << " " << leaves[ leaves.size() -1 -i ].second +1 << endl;
	}

	return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:71:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   71 |  for( int i=0 ; i < leaves.size()/ 2 ; i ++ ){
      |                 ~~^~~~~~~~~~~~~~~~~~

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