Submission #1189016

#	Time	Username	Problem	Language	Result	Execution time	Memory
1189016		yoruonivamp	Network (BOI15_net)	C++20	100 / 100	322 ms	45480 KiB

net

// YoruoniVamp - VTUBE
// Pragma Credit to Discord: pxsithexahydride
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,no-stack-protector,inline-small-functions,inline,unsafe-math-optimizations,omit-frame-pointer,inline-functions-called-once")
#include <bits/stdc++.h>
#pragma GCC target("avx2,fma,popcnt,lzcnt,bmi,bmi2,sse4.2,tune=native")
using namespace std;
#define endl '\n'
#define ll long long
#define ld long double
#define ull unsigned ll
#define cint const int
#define cf const float

cint mxA = 1e6+5, MOD = 1e9+7, INF = 0x3f3f3f3f;
cint d4x[4] = {0, 1, 0, -1}, d4y[4] = {1, 0, -1, 0};
cint d8x[8] = {0, 1, 1, 1, 0, -1, -1, -1}, d8y[8] = {1, 1, 0, -1, -1, -1, 0, 1};

void wait(int ms){
    clock_t endwait;
    endwait = clock() + ms;
    while(clock()<endwait){}
}

int n, m;
vector<vector<int>> adj(int(5e5)+5);
vector<int> deg1;

void dfs(int u, int pre){
    // cout << u << ' ' << pre << endl;
    if(adj[u].size()==1){
        // cout << "DEG1: " << u << endl;
        deg1.emplace_back(u);
    }
    for(auto v: adj[u]){
        if(v!=pre){
            dfs(v,u);
        }
    }
}

void solve(){
    cin >> n;
    for(int i = 1; i <= n-1; i++){
        int a, b; cin >> a >> b;
        adj[a].emplace_back(b);
        adj[b].emplace_back(a);
    }dfs(1,0);
    // for(auto i: deg1) cout << i << ' '; cout << endl;
    cout << (deg1.size()+1)/2 << endl;
    for(int i = 0; i < deg1.size()/2; i++){
        cout << deg1[i] << ' ' << deg1[i+(deg1.size()/2)] << endl;
    }
    if(deg1.size()%2) cout << deg1[0] << ' ' << deg1.back();
    return;
}

int main(){
    cin.tie(nullptr)->sync_with_stdio(0);cout.tie(0);
    // freopen("", "r", stdin);
    // freopen("", "w", stdout);
    int t = 1;
    // cin >> t;
    while(t--) solve();
    return 0;
}

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