Cod sursa(job #2931235)

Utilizator victorzarzuZarzu Victor victorzarzu Data 30 octombrie 2022 18:16:42
Problema Lowest Common Ancestor Scor 40
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.31 kb
#include <bits/stdc++.h>

#define N 100000
#define oo 0x3f3f3f3f

using namespace std;
ifstream f("lca.in");
ofstream g("lca.out");
int n, m;
int mat[20][N];
vector<int> graf[N];
int level[N];

void read() {
  f>>n>>m;
  for(int i = 2;i <= n;++i) {
    f>>mat[0][i];
    graf[mat[0][i]].push_back(i);
  }
  for(int j = 1;(1 << j) <= n;++j) {
    for(int i = 1;i <= n;++i) {
      mat[j][i] = mat[j - 1][mat[j - 1][i]];
    }
  }
}

void dfs(int node, int lvl) {
  level[node] = lvl;
  for(const auto& vecin : graf[node]) {
    if(!level[vecin]) {
      dfs(vecin, lvl + 1);
    }
  }
}

int lca(int x, int y) {
  if(level[x] < level[y]) {
    int temp = x;
    x = y;
    y = temp;
  }

  int logx, logy;
  for(logx = 0;(1 << logx) <= level[x];++logx);
  for(logy = 0;(1 << logy) <= level[y];++logy);

  for(int k = logx;k >= 0;--k) {
    if(level[x] - (1 << k) >= level[y]) {
      x = mat[k][x];
    }
  }

  if(x == y) {
    return x;
  }

  for(int k = logy;k >= 0;--k) {
    if(mat[k][x] && mat[k][x] != mat[k][y]) {
      x = mat[k][x];
      y = mat[k][y];
    }
  }
  return mat[0][x];
}


void solve() {
  dfs(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;
}