警示后人（if你只AC on #1 #3 #11)

void dfs1(long long x, long long f){
	dep[x]=dep[fa[x]]+1;//错误了，此时fa[x]还未赋值
	fa[x]=f;
	siz[x]=1;
	long long ms=-1;
	for(long long i=head[x];~i;i=a[i].w){
		if(a[i].v==fa[x]) continue;
		dfs1(a[i].v, x);
		siz[x]+=siz[a[i].v];
		if(ms<siz[a[i].v])
			ms=siz[a[i].v], son[x]=a[i].v;
	}
}
void dfs1(long long x, long long f){
	fa[x]=f;
	dep[x]=dep[fa[x]]+1;//所以这样才正确
	siz[x]=1;
	long long ms=-1;
	for(long long i=head[x];~i;i=a[i].w){
		if(a[i].v==fa[x]) continue;
		dfs1(a[i].v, x);
		siz[x]+=siz[a[i].v];
		if(ms<siz[a[i].v])
			ms=siz[a[i].v], son[x]=a[i].v;
	}
}