Pagini recente » Cod sursa (job #1896889) | Cod sursa (job #2867958) | Cod sursa (job #1504416) | Cod sursa (job #2341985) | Cod sursa (job #2643515)
#include <fstream>
#include <vector>
using namespace std;
ifstream cin("lca.in");
ofstream cout("lca.out");
vector <int> L[100001];
int log;
int n,a,q,viz[100001],v[100001][20],nivel[100001];
void dfs(int x)
{
a++;
nivel[x]=a;
viz[x]=1;
for(int i=1;i<=log;i++)
v[x][i]=v[v[x][i-1]][i-1];
for(int i:L[x])
if(!viz[i])
dfs(i);
a--;
}
int LCA(int x,int y)
{
int p=log;
if(nivel[x]>nivel[y])
swap(x,y);
while(nivel[y]>nivel[x])
{
if(nivel[y]-(1<<p)>=nivel[x])
y=v[y][p];
p--;
}
if(x==y)
return x;
for(int p=log;p>=0;p--)
{
if(v[x][p]!=v[y][p])
x=v[x][p],y=v[y][p];
}
return v[x][0];
}
int main(){
cin>>n>>q;
while((1<<(log+1))<=n)
log++;
for(int i=2;i<=n;i++)
{
cin>>v[i][0];
L[v[i][0]].push_back(i);
L[i].push_back(v[i][0]);
}
dfs(1);
int x,y ;
while(q--)
{
cin>>x>>y;
cout<<LCA(x,y)<<'\n';
}
return 0;
}