【DFS】Codeforces Round #398 (Div. 2) C. Garland

#include<cstdio>
#include<algorithm>
#include<cstdlib>
using namespace std;
int n,a[1000010],fa[1000010],b[1000010];
int v[1000010],next[1000010],first[1000010],e,root,sum;
void AddEdge(int U,int V)
{
	v[++e]=V;
	next[e]=first[U];
	first[U]=e;
}
void dfs(int U)
{
	b[U]=a[U];
	for(int i=first[U];i;i=next[i])
	  {
	  	dfs(v[i]);
	  	b[U]+=b[v[i]];
	  }
}
void df2(int U,int ance)
{
	if(ance && b[U]==sum/3)
	  {
	  	printf("%d %d\n",min(ance,U),max(ance,U));
	  	exit(0);
	  }
	for(int i=first[U];i;i=next[i])
	  if(ance)
	    df2(v[i],ance);
	  else if(U!=root && b[U]==sum/3*2)
	    df2(v[i],U);
	  else
	    df2(v[i],0);
}
int other;
void df3(int U)
{
	if(b[U]==sum/3 && other)
	  {
	  	printf("%d %d\n",min(other,U),max(other,U));
	  	exit(0);
	  }
	for(int i=first[U];i;i=next[i])
	  df3(v[i]);
	if(U!=root && b[U]==sum/3)
	  other=U;
}
int main()
{
//	freopen("c.in","r",stdin);
	int x;
	scanf("%d",&n);
	for(int i=1;i<=n;++i)
	  {
	  	scanf("%d%d",&x,&a[i]);
	  	sum+=a[i];
	  	if(x)
	  	  {
	  	  	fa[i]=x;
	  	  	AddEdge(x,i);
	  	  }
	  	else
	  	  root=i;
	  }
	if(sum%3!=0)
	  {
	  	puts("-1");
	  	return 0;
	  }
	dfs(root);
	df2(root,0);
	df3(root);
	puts("-1");
	return 0;
}