Cod sursa(job #1918672)

Utilizator adiXMGemene Adrian adiXM Data 9 martie 2017 16:27:14
Problema Lowest Common Ancestor Scor 10
Compilator cpp Status done
Runda Arhiva educationala Marime 1.36 kb
#include <bits/stdc++.h>

using namespace std;
ifstream f("lca.in");
ofstream g("lca.out");
const int nMax = 100003;
vector <int> Graf[nMax];
int dp[24][nMax]; ///al 2 ^ i lea stramos al lui j
int niv[nMax], n, m;
inline void Dpstramosi() {
    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]];
        }
    }
}
inline int Stramos(int x, int y) { ///al y-lea stramos al lui x
    int p = x;
    for(int i = 0; i <= n; i++) {
        if(y & (1 << i)) {
            p = dp[i][p];
        }
    }
    return p;
}
inline void Dfs(int nod, int nivel) {
    niv[nod] = nivel;
    for(const auto &i : Graf[nod]) {
        Dfs(i, nivel + 1);
    }
}
inline int Lca(int x, int y) {
    if(niv[y] > niv[x]) {
        swap(x, y);
    }
    x = Stramos(x, niv[x] - niv[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 x, y;
    f >> n >> m;
    for(int i = 2; i <= n; i++) {
        f >> x;
        dp[0][i] = x;
        Graf[x].push_back(i);
    }
    Dpstramosi();
    Dfs(1, 0);
    for(int i = 1; i <= m; i++) {
        f >> x >> y;
        g << Lca(x, y) << "\n";
    }
    return 0;
}