Cod sursa(job #773694)

Utilizator PlayLikeNeverB4George Marcus PlayLikeNeverB4 Data 2 august 2012 13:24:04
Problema Lowest Common Ancestor Scor 10
Compilator cpp Status done
Runda Arhiva educationala Marime 1.77 kb
#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <ctype.h>
#include <cstring>
#include <ctime>

using namespace std;

#define MAXN 100005
#define MAXLOGN 20
vector<int> graph[MAXN];
int H[MAXN];
int v[3 * MAXN], poz[3 * MAXN];
int lg[3 * MAXN];
int rmq[3 * MAXN][MAXLOGN];
int t, x, y, N, M, vsz;

void parc(int node, int level) {
    poz[node] = vsz;
    H[node] = level;
    v[vsz++] = node;
    for(size_t i = 0; i < graph[node].size(); i++) {
        parc(graph[node][i], level + 1);
        v[vsz++] = node;
    }
}

int lca(int x, int y) {
    int px = poz[x];
    int py = poz[y];
    int k = lg[py - px + 1];

    if(H[rmq[px][k]] < H[rmq[py - (1 << k) + 1][k]])
        return rmq[px][k];
    else
        return rmq[py - (1 << k) + 1][k];
}

int main() {
	freopen("lca.in", "r", stdin);
	freopen("lca.out","w", stdout);

    scanf("%d %d", &N, &M);

    for(int i = 2; i <= N; i++) {
        scanf("%d", &t);
        graph[t].push_back(i);
    }

    parc(1, 0);

    for(int i = 0; i < vsz; i++)
        rmq[i][0] = v[i];
    for(int j = 1; (1 << j) <= vsz; j++)
        for(int i = 0; i + (1 << j) <= vsz; i++)
            if(H[rmq[i][j - 1]] < H[rmq[i + (1 << (j - 1))][j - 1]])
                rmq[i][j] = rmq[i][j - 1];
            else
                rmq[i][j] = rmq[i + (1 << (j - 1))][j - 1];

    lg[1] = 0;
    for(int i = 2; i <= vsz; i++)
        lg[i] = lg[i / 2] + 1;

    for(int i = 0; i < M; i++) {
        scanf("%d %d", &x, &y);

        int res = lca(x, y);

        printf("%d\n", res);
    }

	return 0;
}