제출 #592552

#제출 시각아이디문제언어결과실행 시간메모리
592552ddy888Network (BOI15_net)C++17
0 / 100
6 ms11988 KiB
#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; }
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