AIM Tech Round 3 (Div. 2) E. Centroids

#include<bits/stdc++.h>
#define maxn 400010
#define mod 1000000007
#define ll long long
#define pb push_back
#define fs first
#define se second
using namespace std;
const int INF=1e9+7;

int n;
vector<int> G[maxn];
int fson[maxn],sson[maxn],up[maxn],dw[maxn];
int siz[maxn],ans[maxn];

void dfs(int u,int fa)
{
    siz[u]=1;
    fson[u]=sson[u]=0;
    for(int i=0;i<G[u].size();i++)
    {
        int v=G[u][i];
        if(v==fa) continue;
        dfs(v,u);
        siz[u]+=siz[v];
        if(dw[v]>sson[u]) sson[u]=dw[v];
        if(fson[u]<sson[u]) swap(fson[u],sson[u]);
    }
    dw[u]=fson[u];
    if(siz[u]<=n/2) dw[u]=siz[u];
}

void dfs1(int u,int fa)
{
    if(fa!=-1)
    {
        up[u]=max(up[u],up[fa]);
        if(dw[u]!=fson[fa]) up[u]=max(up[u],fson[fa]);
        else  up[u]=max(up[u],sson[fa]);
        if(n-siz[u]<=n/2) up[u]=n-siz[u];
    }
    int tmp=0;
    for(int i=0;i<G[u].size();i++)
    {
        int v=G[u][i];
        if(v==fa) continue;
        dfs1(v,u);
        if(siz[v]>n/2) tmp=v;
    }
    if(n-siz[u]>n/2) tmp=-1;
    if(!tmp) ans[u]=1;
    else if(tmp>0)
    {
        if(siz[tmp]-dw[tmp]<=n/2) ans[u]=1;
    } 
    else if(n-siz[u]-up[u]<=n/2) ans[u]=1;
}

int main()
{
    cin>>n;
    for(int i=1;i<n;i++)
    {
        int x,y;
        cin>>x>>y;
        G[x].pb(y);
        G[y].pb(x);
    }
    dfs(1,-1);
    dfs1(1,-1);
    for(int i=1;i<=n;i++) printf("%d ",ans[i]);
    printf("\n");
    return 0;
}