제출 #545715

#제출 시각아이디문제언어결과실행 시간메모리
545715SavicSNetwork (BOI15_net)C++17
63 / 100
8 ms9940 KiB
#include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> #include <bits/stdc++.h> using namespace std; using namespace __gnu_pbds; typedef long long ll; typedef long double ld; typedef pair<int,int> pii; typedef pair<ll,ll> pll; typedef pair<ld,ld> pdd; #define ff(i,a,b) for(int i = a; i <= b; i++) #define fb(i,b,a) for(int i = b; i >= a; i--) #define trav(a,x) for (auto& a : x) #define sz(a) (int)(a).size() #define pb push_back #define fi first #define se second #define lb lower_bound #define ub upper_bound #define all(a) a.begin(), a.end() #define rall(a) a.rbegin(), a.rend() mt19937 rng(chrono::steady_clock::now().time_since_epoch().count()); template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; // os.order_of_key(k) the number of elements in the os less than k // *os.find_by_order(k) print the k-th smallest number in os(0-based) const int mod = 998244353; const int inf = 1e9 + 5; const int mxN = 200005; int n; vector<int> g[mxN]; int timer = 0; int in[mxN]; void dfs(int v, int p){ in[v] = ++timer; for(auto u : g[v]){ if(u != p){ dfs(u, v); } } } bool cmp(int s1, int s2){ return in[s1] < in[s2]; } int main() { cin.tie(0)->sync_with_stdio(0); cin >> n; ff(i,1,n - 1){ int u, v; cin >> u >> v; g[u].pb(v); g[v].pb(u); } if(n == 1){ cout << 1 << '\n'; cout << 1 << " " << 1 << '\n'; return 0; } dfs(1, -1); vector<int> leaf; ff(i,1,n)if(sz(g[i]) == 1)leaf.pb(i); sort(all(leaf), cmp); cout << (sz(leaf) + 1) / 2 << '\n'; if(sz(leaf) % 2 == 1){ cout << leaf[0] << " " << leaf.back() << '\n'; leaf.pop_back(); } int K = sz(leaf) / 2; for(int i = 0; i + K < sz(leaf); i++){ cout << leaf[i] << " " << leaf[i + K] << '\n'; } return 0; } /* // probati bojenje sahovski */
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