Submission #484405

#	Time	Username	Problem	Language	Result	Execution time	Memory
484405		MilosMilutinovic	Network (BOI15_net)	C++14	0 / 100	2 ms	2636 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=101000;
int n,sz[N];
VI g[N];
void dfs1(int x,int f) {
	sz[x]=1;
	for (auto u:g[x]) if (u!=f) dfs1(u,x),sz[x]+=sz[u];
}
int dfs2(int x,int f) {
	for (auto u:g[x]) if (u!=f&&sz[u]*2>n) return dfs2(u,x);
	return 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);
	}
	dfs1(1,0);
	int cen=dfs2(1,0);
	printf("%d\n",(SZ(g[cen])+1)/2);
	VI rip; for (auto x:g[cen]) rip.pb(x);
	for (int i=0;i<SZ(rip)-1;i+=2) {
		printf("%d %d\n",rip[i],rip[i+1]);
	}
	if (SZ(rip)%2==1&&SZ(rip)>1) printf("%d %d\n",rip[SZ(rip)-2],rip[SZ(rip)-1]);
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:34:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   34 |  scanf("%d",&n);
      |  ~~~~~^~~~~~~~~
net.cpp:37:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |   scanf("%d%d",&x,&y);
      |   ~~~~~^~~~~~~~~~~~~~

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37