Submission #394616

#	Time	Username	Problem	Language	Result	Execution time	Memory
394616		Return_0	Network (BOI15_net)	C++17	100 / 100	482 ms	40984 KiB

net

// #pragma GCC optimize("Ofast,unroll-loops")
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma,tune=native")

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

typedef int ll;
typedef long double ld;
typedef pair <ll, ll> pll;

#ifdef SINA
#define dbg(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char* name, Arg1&& arg1) { cout << name << " : " << arg1 << std::endl; }
template <typename Arg1, typename... Args> void __f (const char* names, Arg1&& arg1, Args&&... args) {
	const char* comma = strchr(names + 1, ',');cout.write(names, comma - names) << " : " << arg1<<" | ";__f(comma+1, args...); }
#define dbg2(x, j, n) cout<< #x << " : "; output((j), (n), x, 1); cout.flush();
#else
#define dbg(...) 0
#define dbg2(x, j, n) 0
#endif
#define SZ(x) ((ll)((x).size()))
#define File(s, t) freopen(s ".txt", "r", stdin); freopen(t ".txt", "w", stdout);
#define input(j, n, a) for (int _i = (j); _i < (n)+(j); _i++) cin>> a[_i];
#define output(j, n, a, t) for (int _i = (j); _i < (n)+(j); _i++) cout<< a[_i] << (((t) && _i != (n)+(j)-1)? ' ' : '\n');
#define kill(x) return cout<< (x) << endl, 0
#define cl const ll
#define fr first
#define sc second
#define lc (v << 1)
#define rc (lc | 1)
#define mid ((l + r) >> 1)
#define All(x) (x).begin(), (x).end()

cl inf = sizeof(ll) == 4 ? (1e9 + 10) : (3e18), mod = 1e9 + 7, MOD = 998244353;

template <class A,class B> ostream& operator << (ostream& out,const pair<A,B>&a){return out<<'('<<a.first<<", "<<a.second<<')';}
template <class A> ostream& operator << (ostream& out, const vector<A> &a) {
	out<< '['; for (int i = -1; ++i < int(a.size());) out<< a[i] << (i + 1 < int(a.size()) ? ", " : ""); return out<<']'; }
template <class T, typename _t = less <T> > using Tree = tree <T, null_type, _t, rb_tree_tag, tree_order_statistics_node_update>;

cl N = 5e5 + 7;

ll n;
vector <ll> adj [N], vec;

void dfs (cl &v, cl &pr = 0) {
	if (SZ(adj[v]) == 1) vec.push_back(v);
	for (auto &u : adj[v]) if (u != pr) dfs(u, v);
}

int main ()
{
	ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);

	cin>> n;
	for (ll i = 1, v, u; i < n; i++) {
		cin>> v >> u;
		adj[v].push_back(u);
		adj[u].push_back(v);
	}

	for (ll v = 1; v <= n; v++) if (SZ(adj[v]) > 1) { dfs(v); break; }

	n = (SZ(vec) + 1) / 2;
	cout<< n << '\n';
	n = SZ(vec) / 2;
	for (ll i = 0; i + n < SZ(vec); i++) cout<< vec[i] << ' ' << vec[i + n] << '\n';

	// cerr<< "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";

	return 0;
}
/*
6
1 2
2 3
2 4
5 4
6 4

8
1 2
2 3
3 4
4 5
3 6
3 7
3 8

*/

• Subtask 1: 18 / 18
• Subtask 2: 45 / 45
• Subtask 3: 37 / 37