Cod sursa(job #754692)

Utilizator visanrVisan Radu visanr Data 2 iunie 2012 21:50:36
Problema Lowest Common Ancestor Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 1.68 kb
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <vector>
using namespace std;

#define nmax 200010

int n, m, k, Euler[nmax], M[nmax][20], First[nmax], L[nmax];
vector<int> G[nmax];

void dfs(int node, int level)
{
     Euler[++k] = node;
     L[k] = level;
     First[node] = k;
     for(int i = 0; i < G[node].size(); i++)
     {
                dfs(G[node][i], level + 1);
                Euler[++k] = node;
                L[k] = level;
     }
}


void RMQ()
{
     int i, j;
     for(i = 0; i < k; i++) M[i][0] = i;
     for(j = 1; (1 << j) <= k; j++)
     {
           for(i = 0; i + (1 << j) - 1 < k; i++)
           {
                 if(L[M[i][j - 1]] < L[M[i + (1 << (j - 1))][j - 1]])
                 {
                             M[i][j] = M[i][j - 1];
                 }else
                 {
                      M[i][j] = M[i + (1 << (j - 1))][j - 1];
                 }
           }
     }
}


int LCA(int x, int y)
{
    int i, j, k;
    i = First[x];
    j = First[y];
    if(i > j)
    {
         int aux = i;
         i = j;
         j = aux;
    }
    k = (int) log2(j - i + 1);
    if(L[M[i][k]] <= L[M[j - (1 << k) + 1][k]]) return Euler[M[i][k]];
    else return Euler[M[j - (1 << k) + 1][k]];
}

int main()
{
    freopen("lca.in", "r", stdin);
    freopen("lca.out", "w", stdout);
    int i, x, y;
    scanf("%i %i", &n, &m);
    k = -1;
    for(i = 2; i <= n; i++) 
    {
          scanf("%i", &x);
          G[x].push_back(i);
    }
    dfs(1, 0);
    k++;
    RMQ();
    for(i = 0; i < m; i++)
    {
          scanf("%i %i", &x, &y);
          printf("%i\n", LCA(x, y));
    }
    return 0;
}