Submission #592552

#	Time	Username	Problem	Language	Result	Execution time	Memory
592552		ddy888	Network (BOI15_net)	C++17	0 / 100	6 ms	11988 KiB

net

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb push_back
#define fi first
#define si second
#define ar array
typedef pair<int,int> pi;
typedef tuple<int,int,int> ti;  
template<typename T> bool chmin(T &a, T b){return (b < a) ? a = b, 1 : 0;}
template<typename T> bool chmax(T &a, T b){return (b > a) ? a = b, 1 : 0;}
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());

void debug_out() {cerr<<endl;}
template <typename Head, typename... Tail>
void debug_out(Head _H, Tail... _T) {cerr<<" "<<to_string(_H);debug_out(_T...);}
#define debug(...) cerr<<"["<<#__VA_ARGS__<<"]:",debug_out(__VA_ARGS__)

const int MAXN = 500010;

int n;

int cnt = 1;
int in[MAXN];
int pre[MAXN];
vector<int> g[MAXN];

priority_queue<pi, vector<pi>, greater<pi> > mn;
priority_queue<pi> mx;
int done[MAXN];
vector<pi> ans;

void dfs(int x, int p) {
    pre[x] = cnt++; 
    for (auto i: g[x]) {
        if (i == p) continue;
        dfs(i, x);
    }
    if (in[x] == 1) {
        mn.push({pre[x], x});
        mx.push({pre[x], x});
    }
}


int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    cin.exceptions(ios::badbit | ios::failbit);

    cin >> n;
    for (int i = 1; i < n; ++i) {
        int u, v; cin >> u >> v;
        ++in[u], ++in[v];
        g[u].pb(v);
        g[v].pb(u);
    }

    dfs(1, 1);

    int temp = mx.top().si;
    while (mx.size()) {
        pi u = mx.top();
        pi v = mn.top();
        if (done[u.si] || done[v.si]) break;
        if (u.si == v.si) {
            ans.pb({u.si, temp});
            break;
        }
        else ans.pb({u.si, v.si});
        mx.pop(); mn.pop();
        done[u.si] = 1; done[v.si] = 1;
    }

    cout << (int)ans.size() << '\n';
    for (auto i: ans) cout << i.fi << ' ' << i.si << '\n';

    return 0;
}   

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