Codeforces Round #425 (Div. 2), problem: (D) Misha, Grisha and Underground Solution In C/C++

#include<cstdio>
#include<iostream>
using namespace std;
struct Edge{
int to,next;
}e[202020];
int head[101010],cnt=0;
void add(int u,int v)
{
cnt++;
e[cnt].to=v;
e[cnt].next=head[u];
head[u]=cnt;
}
int anc[20][101010];
int dep[101010];
void dfs(int x,int fa)
{
for(int i=head[x];i!=0;i=e[i].next)
{
int to=e[i].to;
if(to!=fa)
{
dep[to]=dep[x]+1;
anc[0][to]=x;
dfs(to,x);
}
}
}

int lca(int u,int v)
{
if(u==v)
return u;
if(dep[u]<dep[v])
swap(u,v);
for(int i=18;i>=0&&dep[u]!=dep[v];i–)
if(dep[anc[i][u]]>=dep[v])
u=anc[i][u];
if(u==v)
return u;
for(int i=18;i>=0;i–)
if(anc[i][u]!=anc[i][v])
{
u=anc[i][u];
v=anc[i][v];
}
return anc[0][u];
}
int dis(int u,int v)
{
int LCA=lca(u,v);
return dep[u]+dep[v]-dep[LCA]-dep[LCA];
}
int main()
{
int n,q;
scanf(“%d%d”,&n,&q);
for(int i=2;i<=n;i++)
{
int p;
scanf(“%d”,&p);
add(i,p);
add(p,i);
}
anc[0][1]=1;
dep[1]=1;
dfs(1,0);
for(int i=1;i<=18;i++)
for(int j=1;j<=n;j++)
anc[i][j]=anc[i-1][anc[i-1][j]];
while(q–)
{
int s,t,f;
scanf(“%d%d%d”,&s,&t,&f);
int mid=1;
int might;
might=lca(s,t);
if(dep[might]>dep[mid])
mid=might;
might=lca(s,f);
if(dep[might]>dep[mid])
mid=might;
might=lca(t,f);
if(dep[might]>dep[mid])
mid=might;
int ans=0;
ans=max(dis(mid,s),max(dis(mid,t),dis(mid,f)));
printf(“%d\n”,ans+1);
}
return 0;
}