Submission #1162197

#	Time	Username	Problem	Language	Result	Execution time	Memory
1162197		LilPluton	Network (BOI15_net)	C++20	100 / 100	226 ms	65788 KiB

net

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ar array
#define all(x) x.begin(), x.end()
#define sortall(x) sort(all(x)) 
#define rep(i,a,b) for(int i = a; i < b; i++)
#define per(i,a,b) for(int i = a; i >= b; i--)
#define trav(a,x) for(auto& a : x)
#define sz(x) (int)(x).size()
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define endl '\n'
#define debug(x) cerr << #x << " = " << x << endl
const int N = 1e6 + 5;

struct BIT{
    int n;
    vector<int>ft;
    void init(int _n){
        n = _n;
        ft.resize(n + 1);
    }
    void update(int x, int val){
        for(; x <= n; x += x & -x){
            ft[x] += val;
        }
    }
    int query(int x){
        int res = 0;
        for(; x > 0; x -= x & -x){
            res += ft[x];
        }
        return res;
    }
    int get(int l,int r){
        return query(r) - query(l - 1);
    }
};
struct DSU{
    int n;
    vector<int> par, siz;
    void init(int _n){
        n = _n + 5;
        par.resize(n);
        siz.resize(n);
        iota(all(par), 0);
        fill(all(siz), 1);
    }
    int find(int x){
        return x == par[x] ? x : par[x] = find(par[x]);
    }
    void unite(int x, int y){
        x = find(x);
        y = find(y);
        if(x != y){
            if(siz[x] < siz[y]) swap(x, y);
            par[y] = x;
            siz[x] += siz[y];
        }
    }
};
vector<int>adj[N];
vector<int>indeg(N);
vector<int>v;
void dfs(int u, int p){
    if(indeg[u] == 1){
        v.push_back(u);
        return;
    }
    for(auto v : adj[u]){
        if(v != p){
            dfs(v, u);
        }
    }
}

void solve(){
    int n;
    cin >> n;
    rep(i, 0, n - 1){
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
        indeg[u]++;
        indeg[v]++;
    }
    rep(i, 1, n + 1){
        if(indeg[i] > 1){
            dfs(i, -1);
            break;
        }
    }
    int ans = sz(v);
    cout << (ans + 1) / 2 << endl;
    rep(i, 0, (ans + 1) / 2){
        cout << v[i] << " " << v[i + (ans) / 2] << endl;
    }
}

signed main() {
    ios::sync_with_stdio(0); cin.tie(0);
    int T = 1;
    while(T--){
        solve();
    }
}

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