Submission #1107531

#	Time	Username	Problem	Language	Result	Execution time	Memory
1107531		koukirocks	Network (BOI15_net)	C++17	100 / 100	300 ms	69320 KiB

net

#include <bits/stdc++.h>
#define speed ios_base::sync_with_stdio(0); cin.tie(0)
#define all(x) (x).begin(),(x).end()
#define F first
#define S second
//#pragma GCC optimize("O3,unroll-loops")
//#pragma GCC target("avx,avx2")
//#pragma GCC target("popcnt")
 
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ldb;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
 
const ll MAX=2e5+10,P=1e9+7;
const ll INF=0x3f3f3f3f,oo=0x3f3f3f3f3f3f3f3f;
const ldb eps=1e-6;
const ldb PI=acos(-1.0);
const int dir[4][2]={{0,1},{0,-1},{1,0},{-1,0}};
template<typename T>
using vvector = vector<vector<T>>;
 
vector<ll> dfs(int v,int p,vvector<int> &G,vector<pii> &ans) {
    vector<ll> lv;
    for (int i:G[v]) {
        if (i==p) continue;
        auto nlv = dfs(i,v,G,ans);
        while (!lv.empty() and !nlv.empty() and lv.size()+nlv.size()>2) {
            ans.emplace_back(lv.back(),nlv.back());
            lv.pop_back();
            nlv.pop_back();
        }
        while (!nlv.empty()) {
            lv.push_back(nlv.back());
            nlv.pop_back();
        }
    }
    if (G[v].size()==1) lv.push_back(v);
    return lv;
}
 
int main() {
    speed;
    int n;
    cin>>n;
    vvector<int> G(n+1);
    for (int i=0;i<n-1;i++) {
        int a,b;
        cin>>a>>b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    int rot=0;
    for (int i=1;i<=n;i++) {
        if (G[i].size()>1) {
            rot=i;
            break;
        }
    }
    vector<pii> ans;
    auto lv = dfs(rot,0,G,ans);
    if (lv.size()==2) ans.emplace_back(lv[0],lv[1]);
    else if (lv.size()==1) ans.emplace_back(lv[0],rot);
    cout<<ans.size()<<"\n";
    for (auto [a,b]:ans) cout<<a<<" "<<b<<"\n"; 
    return 0;
}

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