Submission #592588

#TimeUsernameProblemLanguageResultExecution timeMemory
592588ddy888Network (BOI15_net)C++17
100 / 100
423 ms47660 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; vector<int> g[MAXN]; vector<int> leaf; void dfs(int x, int p) { if ((int)g[x].size() == 1) leaf.pb(x); for (auto i: g[x]) { if (i == p) continue; dfs(i, 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; g[u].pb(v); g[v].pb(u); } dfs(1, 1); int ans = ((int)leaf.size() + 1) / 2; cout << ans << '\n'; if ((int)leaf.size() % 2) leaf.pb(leaf.front()); int j = ans; for (int i = 0; i < ans; ++i) { cout << leaf[i] << ' ' << leaf[j++] << '\n'; } return 0; }
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