Submission #484417

#	Time	Username	Problem	Language	Result	Execution time	Memory
484417		MilosMilutinovic	Network (BOI15_net)	C++14	100 / 100	398 ms	57612 KiB

net

#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef long long ll;
typedef pair<int,int> PII;
typedef double db;
mt19937 mrand(random_device{}());
const ll mod=1000000007;
int rnd(int x) { return mrand() % x;}
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll gcd(ll a,ll b) { return b?gcd(b,a%b):a;}
// head

const int N=501000;
int n;
VI g[N],l;
void dfs(int x,int f) {
	bool lf=true;
	for (auto u:g[x]) {
		if (u!=f) {
			dfs(u,x);
			lf=false;
		}
	}
	if (lf) l.pb(x);
}
int main() {
	scanf("%d",&n);
	rep(i,1,n) {
		int x,y;
		scanf("%d%d",&x,&y);
		g[x].pb(y);
		g[y].pb(x);
	}
	int rt=-1;
	rep(i,1,n+1) if (SZ(g[i])>1) rt=i;
	assert(rt!=-1);
	dfs(rt,0);
	vector<PII> ans;
	for (int i=0;i<SZ(l)/2;i++) {
		ans.pb(mp(l[i],l[SZ(l)/2+i]));
	}
	if (SZ(l)&1) ans.pb(mp(l[0],l.back()));
	printf("%d\n",SZ(ans));
	rep(i,0,SZ(ans)) printf("%d %d\n",ans[i].fi,ans[i].se);
//	if (SZ(l)%2==1&&SZ(l)>1) printf("%d %d\n",l[SZ(l)-2],l[SZ(l)-1]);
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:36:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |  scanf("%d",&n);
      |  ~~~~~^~~~~~~~~
net.cpp:39:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   39 |   scanf("%d%d",&x,&y);
      |   ~~~~~^~~~~~~~~~~~~~

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