Cod sursa(job #1453045)

Utilizator retrogradLucian Bicsi retrograd Data 22 iunie 2015 17:30:59
Problema Lowest Common Ancestor Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 1.43 kb
#include<bits/stdc++.h>

using namespace std;
typedef int var;

#define MAXN 100005

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

void dfs(var node) {
    Heavy[node] = 1;
    In[node] = node;
    var best = 0;
    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];
            In[node] = In[vec];
        }
    }
}

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

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

#define DIM 100000
char buff[DIM];
var poz;
void Read(var &a) {
    while(!isdigit(buff[poz]))
        if(++poz == DIM)
            cin.read(buff, DIM), poz=0;
    a = 0;
    while(isdigit(buff[poz])) {
        a = a * 10 + buff[poz] - '0';
        if(++poz == DIM)
            cin.read(buff, DIM), poz=0;
    }
}


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

    var n, m, p, a, b;
    Read(n); Read(m);
    for(var i=2; i<=n; i++) {
        Read(p);
        G[p].push_back(i);
    }

    D[1] = 1;
    dfs(1);
    PathP[In[1]] = 0;

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