제출 #404165

#제출 시각아이디문제언어결과실행 시간메모리
404165SavicSNetwork (BOI15_net)C++14
100 / 100
506 ms47732 KiB
#include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> #include <bits/stdc++.h> #define fi first #define se second #define pb push_back #define sz(a) (int)a.size() #define all(a) a.begin(), a.end() #define rall(a) a.rbegin(), a.rend() #define ff(i,a,b) for(int i=a;i<=b;i++) #define fb(i,b,a) for(int i=b;i>=a;i--) using namespace std; using namespace __gnu_pbds; typedef long long ll; typedef pair<int,int> pii; const int maxn = 500005; const int inf = 1e9 + 5; 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) int n; vector<int> g[maxn]; vector<int> leaf; void dfs(int v, int p){ if(sz(g[v]) == 1)leaf.pb(v); for(auto u : g[v]){ if(u != p)dfs(u, v); } } int main() { ios::sync_with_stdio(false); cout.tie(nullptr); cin.tie(nullptr); cin >> n; ff(i,1,n - 1){ int u, v; cin >> u >> v; g[u].pb(v); g[v].pb(u); } dfs(1, -1); int len = (sz(leaf) + 1) / 2, add = sz(leaf) / 2; cout << len << endl; ff(i,0,len - 1)cout << leaf[i] << " " << leaf[i + add] << '\n'; return 0; } /** 8 4 1 8 2 1 3 5 7 4 8 6 1 4 7 // probati bojenje sahovski ili slicno **/
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