Pagini recente » Cod sursa (job #937429) | Cod sursa (job #996576) | Cod sursa (job #3192592) | Cod sursa (job #1283663) | Cod sursa (job #1345972)
#include <cstdio>
#include <vector>
#define max(a, b) (a > b ? a : b)
#define NMAX 100005
using namespace std;
int n, m, k;
vector<int>v[NMAX];
int H[NMAX << 1], Lv[NMAX << 1], first[NMAX], lg[NMAX];
int R[NMAX << 2][25];
void dfs(int nod,int niv)
{
H[++k]=nod;
Lv[k]=niv;
first[nod]=k;
for(int it = 0; it < v[nod].size(); ++it)
{
dfs(v[nod][it],niv+1);
H[++k]=nod;
Lv[k]=niv;
}
}
void citire()
{
int x;
freopen("lca.in", "r", stdin);
scanf("%d%d",&n,&m);
for(int i = 2; i <= n; ++i)
{
scanf("%d",&x);
v[x].push_back(i);
}
dfs(1,0);
}
void rmq()
{
int lun;
R[1][0]=1;
for(int i = 2; i <= k; ++i)
{
lg[i]=lg[i/2]+1;
R[i][0]=i;
}
for(int l = 1; 1<<l <= k; ++l)
for(int i = 1; i + (1<<l) <= k; ++i)
{
lun=1<<(l-1);
if(Lv[R[i][l-1]] < Lv[R[i+lun][l-1]]) R[i][l]=R[i][l-1];
else R[i][l]=R[i+lun][l-1];
}
}
int lca(int x, int y)
{
int a=first[x], b=first[y], sol;
if(a > b) swap(a,b);
int dif = b - a +1;
int l=lg[dif];
int sh= dif - (1<<l);
if(Lv[R[a][l]] < Lv[R[a+sh][l]] ) sol=R[a][l];
else sol=R[a+sh][l];
return H[sol];
}
void query()
{
int x,y;
freopen("lca.out", "w",stdout);
for(int i = 1; i <= m; ++i)
{
scanf("%d%d",&x,&y);
printf("%d\n",lca(x,y));
}
}
int main()
{
citire();
rmq();
query();
return 0;
}