Submission #577185

#	Time	Username	Problem	Language	Result	Execution time	Memory
577185		myrcella	Pastiri (COI20_pastiri)	C++17	100 / 100	737 ms	79184 KiB

pastiri

//by szh
#include<bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define pii pair<int,int>
#define pll pair<long long,long long>
#define pb push_back
#define debug(x) cerr<<#x<<"="<<x<<endl
#define pq priority_queue
#define inf 0x3f
#define rep(i,a,b) for (int i=a;i<(b);i++)
#define MP make_pair
#define SZ(x) (int(x.size()))
#define ll long long
#define mod 1000000007
#define ALL(x) x.begin(),x.end()
void inc(int &a,int b) {a=(a+b)%mod;}
void dec(int &a,int b) {a=(a-b+mod)%mod;}
int lowbit(int x) {return x&(-x);}
ll p0w(ll base,ll p) {ll ret=1;while(p>0){if (p%2ll==1ll) ret=ret*base%mod;base=base*base%mod;p/=2ll;}return ret;}

const int maxn = 5e5+10;

int n,m;
int dis[maxn];
bool vis[maxn];
int dep[maxn];
vector <int> sheep;
queue <int> q;
vector <int> edge[maxn];
vector <int> ans;
int a[maxn];

void bfs() {
	while (!q.empty()) {
		int u = q.front();
		q.pop();
		for (int v:edge[u]) if (dis[v]>dis[u]+1) {
			dis[v] = dis[u] + 1;
			q.push(v);
		}
	}
	return;
}

void dfs(int u,int fa) {
	dep[u] = dep[fa]+1;
	for (int v:edge[u]) {
		if (v==fa) continue;
		dfs(v,u);
	}
}

void dfs1(int u,int fa,int mx,int opt) {
	if (dep[u]+dis[u]>mx) {
		mx = dep[u]+dis[u];
		opt = u;
	}
	a[u] = opt;
	for (int v:edge[u]) {
		if (v==fa) continue;
		dfs1(v,u,mx,opt);
	}
}

void cover(int u) {
	vis[u] = true;
	for (int v:edge[u]) {
		if (vis[v] or dis[v]+1!=dis[u]) continue;
		cover(v);
	}
}

int main() {
//	freopen("input.txt","r",stdin);	
	std::ios::sync_with_stdio(false);cin.tie();
	cin>>n>>m;
	memset(dis,0x3f,sizeof(dis));
	rep(i,1,n) {
		int u,v;
		cin>>u>>v;
		edge[u].pb(v);
		edge[v].pb(u);
	}
	rep(i,0,m) {
		int x;
		cin>>x;
		sheep.pb(x);
		q.push(x);
		dis[x] = 0;
	}
	bfs();
	dfs(1,0);
	sort(ALL(sheep),[](const int lhs,const int rhs) {return dep[lhs]>dep[rhs];});
	dfs1(1,0,0,0);
	for (int it:sheep) {
		if (vis[it]) continue;
		cover(a[it]);
		ans.pb(a[it]);
	}
	cout<<SZ(ans)<<"\n";
	for (int it:ans) cout<<it<<" ";
	return 0;
}

• Subtask 1: 8 / 8
• Subtask 2: 18 / 18
• Subtask 3: 23 / 23
• Subtask 4: 51 / 51