Cod sursa(job #1453030)

Utilizator retrogradLucian Bicsi retrograd Data 22 iunie 2015 16:56:54
Problema Lowest Common Ancestor Scor 50
Compilator cpp Status done
Runda Arhiva educationala Marime 1.12 kb
#include<bits/stdc++.h>

using namespace std;
typedef int var;

#define MAXN 100005

var path;
var D[MAXN], PathP[MAXN], Heavy[MAXN], In[MAXN];
vector<var> G[MAXN];

void dfs(var node) {
    Heavy[node] = 1;
    var best = 0, choose = node;
    for(auto vec : G[node]) {
        D[vec] = D[node] + 1;
        dfs(vec);
        Heavy[node] += Heavy[vec];
        PathP[In[vec]] = node;
        if(best > Heavy[vec]) {
            best = Heavy[vec];
            choose = In[vec];
        }

    }
    In[node] = choose;
}

var lca(var a, var b) {
    while(In[a] != In[b])
        if(D[PathP[In[a]]] < D[PathP[In[b]]])
            b = PathP[In[b]];
        else
            a = PathP[In[a]];

    if(D[a] < D[b])
        return a;
    return b;
}

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

    var n, m, p, a, b;
    cin>>n>>m;
    for(var i=2; i<=n; i++) {
        cin>>p;
        G[p].push_back(i);
    }
    D[0] = -1;
    dfs(1);
    PathP[In[1]] = 0;

    while(m--) {
        cin>>a>>b;
        cout<<lca(a, b)<<'\n';
    }
    return 0;
}