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Cod sursa(job #794956)
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<vector>
#define NMax 100005
using namespace std;
vector <int> vec[NMax];
int first[NMax],eu[2*NMax],k,n;
int niv[2*NMax],b[2*NMax][20];
void df_euler (int nod, int lev)
{
eu[++k]=nod;
niv[k]=lev;
first[nod]=k;
for (int i=0; i<vec[nod].size(); i++)
{
df_euler(vec[nod][i],lev+1);
eu[++k]=nod;
niv[k]=lev;
}
}
void rmq ()
{
int i,j;
for (i=1; i<=k; i++)
b[i][0]=i;
for (j=1; (1<<j)<=k; j++)
for (i=1; i+(1<<j)-1<=k; i++)
if (niv[b[i][j-1]] < niv[b[i+(1<<(j-1))][j-1]])
b[i][j]=b[i][j-1];
else b[i][j]=b[i+(1<<(j-1))][j-1];
}
int lca (int x, int y)
{
int st=first[x],dr=first[y],sol,aux;
if (st>dr) swap(st,dr);
aux=log10(dr-st+1)/log10(2);
if (niv[b[st][aux]]<niv[b[dr-(1<<aux)+1][aux]])
sol=b[st][aux];
else sol=b[dr-(1<<aux)+1][aux];
return eu[sol];
}
int main ()
{
int m,i,t,x,y;
freopen("lca.in","r",stdin);
freopen("lca.out","w",stdout);
scanf("%d%d",&n,&m);
for (i=2; i<=n; i++)
{
scanf("%d",&t);
vec[t].push_back(i);
}
df_euler(1,0);
rmq();
for (i=1; i<=m; i++)
{
scanf("%d%d",&x,&y);
printf("%d\n",lca(x,y));
}
return 0;
}