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Cod sursa(job #368816)
#include <fstream>
#include <vector>
#include <bitset>
using namespace std;
#define MAX_N 100005
#define MAX_M 2000005
#define foreach(V) for(typeof (V).begin() it = (V).begin(); it != (V).end(); ++it)
#define nod first
#define ord second
ifstream fin ("lca.in");
ofstream fout ("lca.out");
int N, M, Sol[MAX_M], T[MAX_N], Str[MAX_N];
vector <int> G[MAX_N];
vector <pair<int, int> >Q[MAX_N];
bitset <MAX_N> viz;
void citire()
{
fin >> N >> M;
for(int i = 2; i <= N; ++i)
{
int x;
fin >> x;
G[x].push_back(i);
}
for(int i = 1; i <= M; ++i)
{
int x, y;
fin >> x >> y;
Q[x].push_back(make_pair(y, i));
Q[y].push_back(make_pair(x, i));
}
}
void unite(int x, int y)
{
T[x] = y;
}
int find(int x)
{
int R, y;
for(R = x; R != T[R]; R = T[R]);
while(x != T[x])
{
y = T[x];
T[x] = R;
x = y;
}
return R;
}
void dfs(int nod)
{
T[nod] = nod;
Str[nod] = nod;
foreach(G[nod])
{
int act = *it;
dfs(act);
unite(act, nod);
Str[find(nod)] = nod;
}
viz[nod] = 1;
foreach(Q[nod])
if(viz[it -> nod])
Sol[it -> ord] = Str[find(it -> nod)];
}
int main()
{
citire();
dfs(1);
for(int i = 1; i <= M; ++i)
fout << Sol[i] << "\n";
}