Cod sursa(job #2149019)

Utilizator adiXMGemene Adrian adiXM Data 2 martie 2018 11:34:37
Problema Lowest Common Ancestor Scor 70
Compilator cpp Status done
Runda Arhiva educationala Marime 1.34 kb
#include <bits/stdc++.h>

using namespace std;
ifstream f("lca.in");
ofstream g("lca.out");
const int nMax = 100005;
int dp[23][nMax], nv[nMax];
vector <int> G[nMax];
bool viz[nMax];
inline void Nivel(int nod, int niv) {
    viz[nod] = true;
    nv[nod] = niv;
    for(const auto &v : G[nod]) {
        if(!viz[v]) {
            Nivel(v, niv + 1);
        }
    }
}
inline int Stramos(int x, int y) { ///al y-lea stramos al lui x
    int p = x;
    for(int i = 0; i <= 20; i++) {
        if(y & (1 << i)) {
            p = dp[i][p];
        }
    }
    return p;
}
inline int Lca(int x, int y) {
    if(nv[y] > nv[x]) {
        swap(x, y);
    }
    x = Stramos(x, nv[x] - nv[y]);
    if(x == y) {
        return x;
    }
    for(int i = 20; i >= 0; i--){
        if(dp[i][x] != dp[i][y]) {
            x = dp[i][x];
            y = dp[i][y];
        }
    }
    return dp[0][x];
}
int main()
{
    int n, m, x, y;
    f >> n >> m;
    for(int i = 2; i <= n; i++) {
        f >> x;
        dp[0][i] = x;
        G[x].push_back(i);
    }
    for(int i = 1; (1 << i) <= n; i++) {
        for(int j = 1; j <= n; j++) {
            dp[i][j] = dp[i - 1][dp[i - 1][j]];
        }
    }
    Nivel(1, 0);
    for(int i = 1; i <= m; i++) {
        f >> x >> y;
        g << Lca(x, y) << "\n";
    }
    return 0;
}