Submission #146833

#	Time	Username	Problem	Language	Result	Execution time	Memory
146833		muhammad_hokimiyon	Network (BOI15_net)	C++14	100 / 100	608 ms	58196 KiB

net

#include <bits/stdc++.h>
//#pragma GCC optimize("Ofast")

#define LL long long
#define se second
#define fi first

using namespace std;

const int N = 5e5 + 7;
const int mod = 1e9 + 7;
const int B = sqrt(N);

int n;
bool used[N];
vector < int > v[N];
vector < int > ans;

void dfs( int x , int p )
{
    if( v[x].size() == 1 && !used[x] ){
        ans.push_back(x);
    }
    used[x] = true;
    for( auto y : v[x] ){
        if( y == p )continue;
        dfs(y , x);
    }
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    //freopen( "input.txt" , "r" , stdin );
    //freopen( "output.txt" , "w" , stdout );

    cin >> n;
    for( int i = 1; i < n; i++ ){
        int x,y;
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    int x = 1;
    for( int i = 1; i <= n; i++ ){
        if( v[i].size() > 1 ){
            x = i;
        }
    }
    dfs(x , x);
    int k = (ans.size() + 1) / 2;
    cout << ( (int)ans.size() + 1 ) / 2 << "\n";
    for( int i = 0; i < ( ans.size() + 1) / 2; i++ ){
        cout << ans[i] << " " << ans[ (i + k) % (int)ans.size() ] << "\n";
    }
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:54:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for( int i = 0; i < ( ans.size() + 1) / 2; i++ ){
                     ~~^~~~~~~~~~~~~~~~~~~~~~~

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