Mai intai trebuie sa te autentifici.
Cod sursa(job #1671371)
Utilizator | Data | 1 aprilie 2016 16:46:53 | |
---|---|---|---|
Problema | Lowest Common Ancestor | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 1.33 kb |
#include <fstream>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#define pi pair<int, int>
#define mp make_pair
#define pb push_back
using namespace std;
ifstream in("lca.in");
ofstream out("lca.out");
const int N = 100100;
const int M = 2000010;
int f[N], true_f[N];
bool marked[N];
vector<int> g[N];
vector<pi> query[N];
int qans[M];
int _find(int x) {
if(x != f[x]) {
f[x] = _find(f[x]);
}
return f[x];
}
void _merge(int x, int y) {
int rx = _find(x), ry = _find(y);
if(rand() & 1) {
f[rx] = ry;
}
else {
f[ry] = rx;
}
}
void offlineLca(int x) {
f[x] = x;
true_f[x] = x;
random_shuffle(g[x].begin(), g[x].end());
for(int i = 0; i < g[x].size(); i++) {
offlineLca(g[x][i]);
_merge(x, g[x][i]);
true_f[_find(x)] = x;
}
marked[x] = 1;
for(auto q : query[x]) {
if(marked[q.first]) {
qans[q.second] = true_f[_find(q.first)];
}
}
}
int main() {
int n, m, i, x, y;
in >> n >> m;
for(i = 2; i <= n; i++) {
in >> x;
g[x].pb(i);
}
for(i = 1; i <= m; i++) {
in >> x >> y;
query[x].pb(mp(y, i));
query[y].pb(mp(x, i));
}
offlineLca(1);
for(i = 1; i <= m; i++) {
out << qans[i] << '\n';
}
}