Submission #924950

#	Time	Username	Problem	Language	Result	Execution time	Memory
924950		Faisal_Saqib	Cat in a tree (BOI17_catinatree)	C++17	100 / 100	687 ms	42832 KiB

catinatree

#include <iostream>
#include <vector>
#include <bitset>
#include <map>
using namespace std;
const int N=2e5+10;
const int LG=18;
int n,d;
int pw2[LG];
int par[N][LG];
vector<int> ma[N],vep[N];
int part[N];
int h[N],dist[N],sz[N];
bitset<N> dead;
int cn;
void dfs(int x,int p=0)
{
	h[x]=h[p]+1;
	vep[h[x]].push_back(x);
	sz[x]=1;
	par[x][0]=p;
	for(int j=1;j<LG;j++)
		par[x][j]=par[par[x][j-1]][j-1];
	for(int y:ma[x])
	{
		if(y!=p)
		{
			dfs(y,x);
			sz[x]+=sz[y];
		}
	}
}
int find_centriod(int x,int p=0)
{
	for(int y:ma[x])
	{
		if(y!=p and !dead[y] and sz[y]>(cn/2))
		{
			sz[x]-=sz[y];
			sz[y]+=sz[x];
			return find_centriod(y,x);
		}
	}
	return x;
}
int solve(int x)
{
	cn=sz[x];
	int c=find_centriod(x);
	dead[c]=1;
	for(int y:ma[c])
		if(!dead[y])
			part[solve(y)]=c;
	return c;
}
// map<pair<int,int>,int> memo;
int dist1(int x,int y)
{
	if(h[x]<h[y])
		swap(x,y);
	int ans=h[x]+h[y];
	for(int j=LG-1;j>=0;j--)
	{
		if(h[par[x][j]]>=h[y])
		{
			x=par[x][j];
		}
	}
	for(int j=LG-1;j>=0;j--)
	{
		if(par[x][j]!=par[y][j])
		{
			x=par[x][j];
			y=par[y][j];
		}
	}
	if(x!=y)
		x=par[x][0];
	return ans-(2*h[x]);
}
void color(int st)
{
	// cout<<"Marked "<<st<<endl;
	int x=st;
	while(x>0)
	{
		dist[x]=min(dist[x],dist1(x,st));	
		x=part[x];
	}
}
int query(int st)
{
	int x=st;
	int ans=dist[x];
	while(x>0)
	{
		ans=min(ans,dist1(x,st)+dist[x]);
		x=part[x];
	}
	return ans;
}
int main()
{
	cin.tie(0);
	cout.tie(0);
	ios::sync_with_stdio(0);
	pw2[0]=1;
	for(int i=1;i<LG;i++)
		pw2[i]=(pw2[i-1]*2ll);
	cin>>n>>d;
	for(int i=2;i<=n;i++)
	{
		int p;
		cin>>p;
		p++;
		ma[p].push_back(i);
		ma[i].push_back(p);
	}
	int ans=0;
	for(int j=1;j<=n;j++)
		dist[j]=1e9;
	dfs(1);
	solve(1);
	for(int cur_h=n;cur_h>=1;cur_h--)
	{
		for(int v:vep[cur_h])
		{
			if(query(v)>=d)
			{
				ans++;
				color(v);
			}
		}
	}
	cout<<ans<<'\n';
	return 0;
}

• Subtask 1: 11 / 11
• Subtask 2: 40 / 40
• Subtask 3: 49 / 49