Cod sursa(job #2931361)

Utilizator victorzarzuZarzu Victor victorzarzu Data 30 octombrie 2022 23:05:01
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.44 kb
#include <bits/stdc++.h>

#define N 100000 + 5 

using namespace std;
ifstream f("lca.in");
ofstream g("lca.out");
int n, m, pos;
int t[N], heavy[N], seq[N], position[N], level[N], size[N];
vector<int> graf[N];

void read() {
  f>>n>>m;
  for(int i = 2;i <= n;++i) {
    f>>t[i];
    graf[t[i]].push_back(i);
    graf[i].push_back(t[i]);
  }
}

void dfs(int node, int parent) {
  level[node] = level[parent] + 1;
  size[node] = 1;

  int maxim = 0;
  for(const auto& vecin : graf[node]) {
    if(vecin != t[node]) {
      dfs(vecin, node);
      size[node] += size[vecin];
      if(maxim < size[vecin]) {
        maxim = size[vecin];
        heavy[node] = vecin;
      }
    }
  }
}

void decompose(int node, int superior) {
  position[node] = pos++;
  seq[node] = superior;
  if(heavy[node]) {
    decompose(heavy[node], superior);
  }
  for(const auto& vecin : graf[node]) {
    if(vecin != t[node] && vecin != heavy[node]) {
      decompose(vecin, vecin);
    }
  }
}

int lca(int x, int y) {
  while(seq[x] != seq[y]) {
    if(position[seq[x]] < position[seq[y]]) {
      int temp = x;
      x = y;
      y = temp;
    }
    x = t[seq[x]];
  }
  if(level[x] > level[y]) {
    return y;
  }
  return x;
}

void solve() {
  dfs(1, 0);
  decompose(1, 1);

  int x, y;
  for(int i = 1;i <= m;++i) {
    f>>x>>y;
    g<<lca(x, y)<<'\n';
  }
}


int main() {
  read();
  solve();
  return 0;
}