제출 #633974

#제출 시각아이디문제언어결과실행 시간메모리
633974radalNetwork (BOI15_net)C++17
0 / 100
1 ms2644 KiB
#include <bits/stdc++.h> #pragma GCC target("sse,sse2") #pragma GCC optimize("unroll-loops,O3") #define rep(i,l,r) for (int i = l; i < r; i++) #define repr(i,r,l) for (int i = r; i >= l; i--) #define X first #define Y second #define all(x) (x).begin() , (x).end() #define pb push_back #define endl '\n' #define debug(x) cerr << #x << " : " << x << endl; using namespace std; typedef long long ll; typedef long double ld; typedef pair<int,int> pll; constexpr int N = 1e5+20,mod = 1e9+7,inf = 1e9+10; inline int mkay(int a,int b){ if (a+b >= mod) return a+b-mod; if (a+b < 0) return a+b+mod; return a+b; } inline int poww(int a,int k){ if (k < 0) return 0; int z = 1; while (k){ if (k&1) z = 1ll*z*a%mod; a = 1ll*a*a%mod; k /= 2; } return z; } vector<int> adj[N]; int tin[N],T; bool cmp(int u,int v){ return (tin[u] < tin[v]); } void dfs(int v,int p){ tin[v] = T++; for(int u : adj[v]) if (u != p) dfs(u,v); } int main(){ ios_base :: sync_with_stdio(0); cin.tie(0); int n,ans = 0; cin >> n; rep(i,1,n){ int u,v; cin >> u >> v; adj[u].pb(v); adj[v].pb(u); } dfs(1,0); vector<int> ve; rep(i,1,n+1) if (adj[i].size() == 1){ ans++; ve.pb(i); } cout << (ans+1)/2; sort(all(ve),cmp); rep(i,0,ans){ if (i == ans-i-1){ cout << ve[i] << ' ' << ve[0] << endl; continue; } if (i > ans-i-1) break; cout << ve[i] << ' ' << ve[ans-i-1] << endl; } }
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