Pagini recente » Cod sursa (job #2606098) | Cod sursa (job #2625161) | Cod sursa (job #109184) | Cod sursa (job #1302646) | Cod sursa (job #3321994)
#include <bits/stdc++.h>
#define NMAX 100001
#define LOG 20
using namespace std;
ifstream in("lca.in");
ofstream out("lca.out");
vector<int> fii[NMAX];
int nivel[NMAX];
int stra[LOG][NMAX];
void dfs(int nod)
{
for(auto& fiu : fii[nod])
{
nivel[fiu]=1+nivel[nod];
dfs(fiu);
}
}
int up(int nod, int k) ///returneaza al k-lea stramos al lui nod
{
for(int e=LOG-1; e>=0; e--)
{
if((1<<e)<=k)
{
nod=stra[e][nod];
k-=(1<<e);
}
}
return nod;
}
int lca(int nod1, int nod2)
{
if(nivel[nod1]<nivel[nod2]) swap(nod1, nod2);
if(nivel[nod1]<nivel[nod2]) swap(nod1, nod2);
nod1=up(nod1, nivel[nod1]-nivel[nod2]); ///aducem cele doua noduri la acelasi nivel
if(nod1==nod2) return nod1;
for(int e=LOG-1; e>=0; e--)
{
if(stra[e][nod1]!=stra[e][nod2])
{
nod1=stra[e][nod1];
nod2=stra[e][nod2];
}
}
return stra[0][nod1];
}
int main()
{
int n, m;
in >> n >> m;
for(int i=2; i<=n; i++)
{
in >> stra[0][i];
fii[stra[0][i]].push_back(i);
}
for(int e=1; e<LOG; e++)
{
for(int i=1; i<=n; i++)
stra[e][i]=stra[e-1][stra[e-1][i]];
}
dfs(1);
while(m--)
{
int u, v;
in >> u >> v;
out << lca(u, v) << "\n";
}
return 0;
}