Submission #640554

#	Time	Username	Problem	Language	Result	Execution time	Memory
640554		sondos225	Network (BOI15_net)	C++17	100 / 100	412 ms	49092 KiB

net

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T>using ordered_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;//find_by_order(ind);//order_of_key()
#define int long long
#define fast ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL);
#define pb emplace_back
#define pf emplace_front
#define yes "YES"
#define no "NO"
#define bigg INT_MAX
#define mp make_pair
#define mt make_tuple
#define debug(x) cout<<(#x)<<" = " <<x<<endl;
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define sz size()
#define nn '\n'
#define mms(x,y) memset(x,y,sizeof(x))
#define forr(i,j,n) for (int i=j; i<n; i++)
#define forn(i,j,n) for (int i=j; i>n; i--)
#define cinn(x,y) for(int i=0; i<y; i++) cin>>x[i];
#define fi first
#define se second
#define la "LA"
#define pii pair<int,int>
// to use cmd ctrl+shift+c then g++ name.cpp -o name2.exe then name2 then input
//ctrl+shift+p to open search
//shift+alt+a stack comment2
///power function works in log2b
// int pwr(int a, int b)
// {
//   int po = 1;
//   while ( b )
//   {
//          if ( b & 1 )
//          {
//            po = po * a;
//            --b;
//          }
//          a = a*a;
//          b = b/2;
//   }
//   return po;
// }
vector <int> a[500001];
vector <int> leaf;
bool vis[500001];
void dfs(int i)
{
    vis[i]=1;
    if (a[i].sz==1) leaf.pb(i);
    forr(j,0,a[i].sz)
    {
        if(!vis[a[i][j]]) dfs(a[i][j]);
    }
    return;
}
signed main()
{
    fast
    //  #ifndef LOCAL
    //  freopen("in.txt","r",stdin);
    //  freopen("out.txt","w",stdout);
    //  #endif
    int n;
    cin>>n;
    forr(i,0,n-1)
    {
        int x,y;
        cin>>x >>y;
        a[x].pb(y);
        a[y].pb(x);
    }
    dfs(1);
    int cnt=leaf.sz;
    // cout<<leaf.sz<<endl<<endl;
    int i=0;
  //j=cnt-1;
    cout<<(cnt/2)+(cnt%2)<<nn;
    while(cnt>0)
    {
        // cout<<yes<<cnt<<endl;
        if (cnt==1)
        {
            
            cout<<leaf[i]<<' '<<leaf[0]<<nn;
        }
        else
        {
            //not 2 adjacent
          //if wrong try idea 2
          //cout<<i<<' '<<j<<endl;
            cout<<leaf[i]<<' '<<leaf[(leaf.sz/2)+(leaf.sz%2)+i]<<nn;
            i++;
        }
        cnt-=2;
    }
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'void dfs(long long int)':
net.cpp:22:36: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 | #define forr(i,j,n) for (int i=j; i<n; i++)
      |                                    ^
net.cpp:55:5: note: in expansion of macro 'forr'
   55 |     forr(j,0,a[i].sz)
      |     ^~~~

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