Pagini recente » Cod sursa (job #1167011) | Cod sursa (job #2881419) | Cod sursa (job #1794699) | Cod sursa (job #2090822) | Cod sursa (job #3215651)
#include <bits/stdc++.h>
#pragma optimize GCC ("Ofast")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
///#include <tryhardmode>
///#include <GODMODE::ON>
using namespace std;
#define cin fin
#define cout fout
ifstream fin ("lca.in");
ofstream fout ("lca.out");
const int NMAX=1e5+5;
vector<int>v[NMAX];
int lvl[NMAX];
int asc[25][NMAX];
void dfs(int p,int tata)
{
int e;
lvl[p]=lvl[tata]+1;
for(e=1;e<=20;e++)
asc[e][p]=asc[e-1][asc[e-1][p]];
for(auto i:v[p])
{
if(i!=tata)
{
asc[0][i]=p;
dfs(i,p);
}
}
}
int lca(int x,int y)
{
int level,e;
if(lvl[x]<lvl[y])
swap(x,y);
level=lvl[x]-lvl[y];
for(e=20;e>=0;e--)
{
if(level & (1<<e))
x=asc[e][x];
}
if(x==y)
return x;
for(e=20;e>=0;e--)
{
if(asc[e][x]!=asc[e][y])
{
x=asc[e][x];
y=asc[e][y];
}
}
return asc[0][x];
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int n,q,i,j;
cin>>n>>q;
for(i=2;i<=n;i++)
{
int x;
cin>>x;
v[i].push_back(x);
v[x].push_back(i);
}
dfs(1,0);
while(q--)
{
int x,y;
cin>>x>>y;
cout<<lca(x,y)<<"\n";
}
return 0;
}