Submission #1149851

#	Time	Username	Problem	Language	Result	Execution time	Memory
1149851		dosts	Network (BOI15_net)	C++20	63 / 100	4 ms	7496 KiB

net

#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3,unroll-loops")
using namespace std;
#define int long long
#define pii pair<int,int>
#define ff first
#define ss second
#define sp << " " <<    
#define all(cont) cont.begin(),cont.end()
#define vi vector<int>

const int inf = 1e17,N = 3e5+1,MOD = 1e9+7,BL = 1000;


vi edges[N];

vi leaf;
void leadfs(int node,int p) {
    for (auto it : edges[node]) {
        if (it == p) continue;
        leadfs(it,node);
    }
    if (edges[node].size() == 1) leaf.push_back(node);
}


void solve() { 
    int n;
    cin >> n;
    for (int i=1;i<n;i++) {
        int a,b;
        cin >> a >> b;
        edges[a].push_back(b);
        edges[b].push_back(a);
    }
    int root = 1;
    for (int i=1;i<=n;i++) {
        if (edges[i].size() == 1) continue;
        root = i;
    }
    leadfs(root,root);
    cout << (leaf.size()+1)/2 << '\n';
    for (int i=0;i<leaf.size()/2;i++) {
        cout << leaf[i] sp leaf[i+leaf.size()/2] << '\n';
    }
    if (leaf.size()%2) cout << leaf[0] sp leaf.back() << '\n';
}

int32_t main() { 
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    #ifdef Dodi 
        freopen("in.txt","r",stdin);
        freopen("out.txt","w",stdout);
    #endif
    int t = 1;
    //cin >> t;
    while (t --> 0) solve();
}

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