Cod sursa(job #1292838)

Utilizator Al3ks1002Alex Cociorva Al3ks1002 Data 14 decembrie 2014 20:46:33
Problema Lowest Common Ancestor Scor 70
Compilator cpp Status done
Runda Arhiva educationala Marime 1.68 kb
#include<cstdio>
#include<fstream>
#include<iostream>
#include<iomanip>
#include<algorithm>
#include<vector>
#include<bitset>
#include<deque>
#include<queue>
#include<set>
#include<map>
#include<cmath>
#include<cstring>
#include<ctime>
#include<cstdlib>
#include<unordered_map>

#define ll long long
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define pll pair<ll,ll>

using namespace std;

const int nmax = 100005;
const int lmax = 17;

int n, q, x, y, i, j, dif, lim, logg, f[lmax][nmax], lev[nmax];

vector<int> v[nmax];

void dfs(int x)
{
    for(auto it : v[x])
    {
        lev[it] = lev[x] + 1;
        dfs(it);
    }
}
int main()
{
    freopen("lca.in", "r", stdin);
    freopen("lca.out", "w", stdout);

    scanf("%d%d", &n, &q);

    for(i = 2; i <= n; i++)
    {
        scanf("%d", &f[0][i]);
        v[f[0][i]].push_back(i);
    }

    for(i = 1; (1 << i) <= n; i++)
        for(j = 1; j <= n; j++)
            f[i][j] = f[i - 1][f[i - 1][j]];

    lev[1] = 1;
    dfs(1);

    for(lim = 1, logg = 0; lim <= n; lim *= 2, logg++);
    logg--;

    for(; q; q--)
    {
        scanf("%d%d", &x, &y);

        if(lev[x] > lev[y])
            swap(x, y);

        dif = lev[y] - lev[x];

        for(i = 0; i <= logg; i++)
            if((1 << i) & dif)
                y = f[i][y];

        if(x == y)
        {
            printf("%d\n", x);
            continue;
        }

        for(i = logg; i >= 0; i--)
            if(f[i][x] != f[i][y])
            {
                x = f[i][x];
                y = f[i][y];
            }

        printf("%d\n", f[0][x]);
    }

    return 0;
}