Cod sursa(job #3231819)

Utilizator rapidu36Victor Manz rapidu36 Data 27 mai 2024 20:23:41
Problema Lowest Common Ancestor Scor 0
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.45 kb
#include <fstream>
#include <vector>

using namespace std;

const int N = 1e5;
const int L = 16;

int t_in[N+1], t_out[N+1], s[L+1][N+1], n, timp;
vector <int> fii[N+1];

void constructie_s()
{
    for (int i = 1; (1 << i) <= n; i++)
    {
        for (int j = 1; j <= n; j++)
        {
            s[i][j] = s[i-1][s[i-1][j]];
        }
    }
}

void dfs(int x)
{
    t_in[x] = ++timp;
    for (auto y: fii[x])
    {
        dfs(y);
    }
    t_out[x] = ++timp;
}

bool este_stramos(int x, int y)
{
    return (t_in[x] <= t_in[y] && t_out[y] <= t_out[x]);
}

int lca(int x, int y)
{
    ///cautam cel mai de sus (de pe cel mai mic nivel) stramos al lui x care NU e stramos al lui y
    if (este_stramos(x, y))
    {
        return x;
    }
    int pas = L;
    while (pas >= 0)
    {
        if (s[pas][x] != 0 && !este_stramos(s[pas][x], y))
        {
            x = s[pas][x];
        }
        pas--;
    }
    return s[0][x];///tatal celui mai indepartat stramos al lui x initial care NU e stramos pentru y
}

int main()
{
    ifstream in("lca.in");
    ofstream out("lca.out");
    int q;
    in >> n >> q;
    for (int j = 2; j <= n; j++)
    {
        in >> s[0][j];
        fii[s[0][j]].push_back(j);
    }
    timp = 0;
    dfs(1);
    for (int i = 0; i < q; i++)
    {
        int x, y;
        in >> x >> y;
        out << lca(x, y) << "\n";
    }
    in.close();
    out.close();
    return 0;
}