Submission #127521

#	Time	Username	Problem	Language	Result	Execution time	Memory
127521		miguel	Network (BOI15_net)	C++14	100 / 100	641 ms	49712 KiB

net

#include<bits/stdc++.h>
using namespace std;
#define rc(x) return cout<<x<<endl,0
#define pb push_back
#define dbg(x) cout << #x << '=' << x << '\n';
#define ll long long
#define sz size()
#define x first
#define y second
#define pi pair <int, int>
#define pii pair <int, pi>
#define vi vector <int>
const ll mod = 1e9 + 7;
int n, deg[500001];
vector <int> g[500001];
vector <int> leaves;

void dfs(int cur, int p){
    //if(deg[cur]==1) cout<<p<<" "<<cur<<" ";
    if(deg[cur]==1) leaves.pb(cur);
    for(int i: g[cur]){
        if(i!=p) dfs(i, cur);
    }
}


int32_t main(){
    ios_base :: sync_with_stdio(0); cin.tie(); cout.tie();
    cin>>n;
    for(int i=1; i<=n-1; i++){
        int x, y;
        cin>>x>>y;
        g[x].pb(y);
        g[y].pb(x);
        deg[x]++, deg[y]++;
    }
    dfs(1, 0);
    int xd=(leaves.size()+1)/2;
    cout<<xd<<"\n";
    for(int i=0; i<xd; i++) cout<<leaves[i]<<" "<<leaves[i+leaves.size()/2]<<"\n";
}

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