Problem p02373 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it, X) for (auto it = (X).begin(); it != (X).end(); it++)
#define numa(x, a) for (auto x : a)
#define ite iterator
#define mp make_pair
#define mt make_tuple
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define pb push_back
#define pf push_front
#define sec second
#define sz(x) ((int)(x).size())
#define ALL(c) (c).begin(), (c).end()
#define gcd(a, b) __gcd(a, b)
#define endl "\\n"
using namespace std;
template <int POS, class TUPLE>
void deploy(std::ostream &os, const TUPLE &tuple) {}
template <int POS, class TUPLE, class H, class... Ts>
void deploy(std::ostream &os, const TUPLE &t) {
  os << (POS == 0 ? "" : ", ") << get<POS>(t);
  deploy<POS + 1, TUPLE, Ts...>(os, t);
}
template <class T>
std::ostream &operator<<(std::ostream &os, std::vector<T> &v) {
  int remain = v.size();
  os << "{";
  for (auto e : v)
    os << e << (--remain == 0 ? "}" : ", ");
  return os;
}
template <class T> std::ostream &operator<<(std::ostream &os, std::set<T> &v) {
  int remain = v.size();
  os << "{";
  for (auto e : v)
    os << e << (--remain == 0 ? "}" : ", ");
  return os;
}
template <class T, class K>
std::ostream &operator<<(std::ostream &os, std::map<T, K> &mp) {
  int remain = mp.size();
  os << "{";
  for (auto e : mp)
    os << "(" << e.first << " -> " << e.second << ")"
       << (--remain == 0 ? "}" : ", ");
  return os;
}
#define DEBUG1(var0)                                                           \\
  { std::cerr << (#var0) << "=" << (var0) << endl; }
#define DEBUG2(var0, var1)                                                     \\
  {                                                                            \\
    std::cerr << (#var0) << "=" << (var0) << ", ";                             \\
    DEBUG1(var1);                                                              \\
  }
#define DEBUG3(var0, var1, var2)                                               \\
  {                                                                            \\
    std::cerr << (#var0) << "=" << (var0) << ", ";                             \\
    DEBUG2(var1, var2);                                                        \\
  }
#define DEBUG4(var0, var1, var2, var3)                                         \\
  {                                                                            \\
    std::cerr << (#var0) << "=" << (var0) << ", ";                             \\
    DEBUG3(var1, var2, var3);                                                  \\
  }
typedef long long ll;

/*
//*********************************
//O(n)のLCA
#define MAX_V 100100
vector <int> edge[MAX_V];
int root;
int parent[MAX_V];
int depth[MAX_V];
int V;
void dfs(int v,int p,int d){
  parent[v] = p;
  depth[v] = d;
  for(int i = 0;i < sz(edge[v]);i++){
    if(edge[v][i] != p){
      dfs(edge[v][i],v,d+1);
    }
  }
}

void init(){
  //parentとdepthを初期化
  dfs(root,-1,0);
}

int LCA(int u,int v){//uとvのLCAを求める
  while(depth[u] > depth[v]){
    u = parent[u];
  }
  while(depth[v] > depth[u]){
    v = parent[v];
  }
  while(u != v){
    u = parent[u];
    v = parent[v];
  }
  return u;
}
//*********************************

*/

//*********************************
// O(log n)アルゴリズム
// O(nlogn)のメモリが必要
#define MAX_V 100100
#define MAX_LOG_V 32
vector<int> edge[MAX_V];
int root;
int parent[MAX_LOG_V][MAX_V];
int depth[MAX_V];
int V;

void dfs(int v, int p, int d) {
  parent[0][v] = p;
  depth[v] = d;
  for (int i = 0; i < edge[v].size(); i++) {
    if (edge[v][i] != p) {
      dfs(edge[v][i], v, d + 1);
    }
  }
}

void init() {
  // parent[0]とrootを初期化
  dfs(root, -1, 0);
  // parentを初期化する
  for (int k = 0; k + 1 < MAX_LOG_V; k++) {
    for (int v = 0; v < V; v++) {
      if (parent[k][v] < 0) {
        parent[k + 1][v] = -1;
      } else {
        parent[k + 1][v] = parent[k][parent[k][v]];
      }
    }
  }
}

int LCA(int u, int v) {
  if (depth[u] > depth[v]) {
    swap(u, v);
  }

  for (int k = 0; k < MAX_LOG_V; k++) {
    if ((depth[v] - depth[u]) >> k & 1) {
      v = parent[k][v];
    }
  }
  if (u == v) {
    return u;
  }
  for (int k = MAX_LOG_V - 1; k >= 0; k--) {
    if (parent[k][u] != parent[k][v]) {
      u = parent[k][u];
      v = parent[k][v];
    }
  }
  return parent[0][u];
}

//*********************************

int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cin >> V;
  rep(i, V) {
    int x;
    cin >> x;
    rep(j, x) {
      int y;
      cin >> y;
      edge[i].pb(y);
    }
  }
  root = 0;
  init();
  int Q;
  cin >> Q;
  rep(i, Q) {
    int x, y;
    cin >> x >> y;
    cout << LCA(x, y) << endl;
  }
  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it, X) for (auto it = (X).begin(); it != (X).end(); it++)
#define numa(x, a) for (auto x : a)
#define ite iterator
#define mp make_pair
#define mt make_tuple
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define pb push_back
#define pf push_front
#define sec second
#define sz(x) ((int)(x).size())
#define ALL(c) (c).begin(), (c).end()
#define gcd(a, b) __gcd(a, b)
#define endl "\\n"
using namespace std;
template <int POS, class TUPLE>
void deploy(std::ostream &os, const TUPLE &tuple) {}
template <int POS, class TUPLE, class H, class... Ts>
void deploy(std::ostream &os, const TUPLE &t) {
  os << (POS == 0 ? "" : ", ") << get<POS>(t);
  deploy<POS + 1, TUPLE, Ts...>(os, t);
}
template <class T>
std::ostream &operator<<(std::ostream &os, std::vector<T> &v) {
  int remain = v.size();
  os << "{";
  for (auto e : v)
    os << e << (--remain == 0 ? "}" : ", ");
  return os;
}
template <class T> std::ostream &operator<<(std::ostream &os, std::set<T> &v) {
  int remain = v.size();
  os << "{";
  for (auto e : v)
    os << e << (--remain == 0 ? "}" : ", ");
  return os;
}
template <class T, class K>
std::ostream &operator<<(std::ostream &os, std::map<T, K> &mp) {
  int remain = mp.size();
  os << "{";
  for (auto e : mp)
    os << "(" << e.first << " -> " << e.second << ")"
       << (--remain == 0 ? "}" : ", ");
  return os;
}
#define DEBUG1(var0)                                                           \\
  { std::cerr << (#var0) << "=" << (var0) << endl; }
#define DEBUG2(var0, var1)                                                     \\
  {                                                                            \\
    std::cerr << (#var0) << "=" << (var0) << ", ";                             \\
    DEBUG1(var1);                                                              \\
  }
#define DEBUG3(var0, var1, var2)                                               \\
  {                                                                            \\
    std::cerr << (#var0) << "=" << (var0) << ", ";                             \\
    DEBUG2(var1, var2);                                                        \\
  }
#define DEBUG4(var0, var1, var2, var3)                                         \\
  {                                                                            \\
    std::cerr << (#var0) << "=" << (var0) << ", ";                             \\
    DEBUG3(var1, var2, var3);                                                  \\
  }
typedef long long ll;

#define MAX_V 100100
//*********************************
// 一度のクエリ処理だけならO(n)のLCA
vector<int> edge[MAX_V];
int root;
int parent[MAX_V];
int depth[MAX_V];
int V;
void dfs(int v, int p, int d) {
  parent[v] = p;
  depth[v] = d;
  for (int i = 0; i < sz(edge[v]); i++) {
    if (edge[v][i] != p) {
      dfs(edge[v][i], v, d + 1);
    }
  }
}

void init() {
  // parentとdepthを初期化
  dfs(root, -1, 0);
}

int LCA(int u, int v) { // uとvのLCAを求める
  while (depth[u] > depth[v]) {
    u = parent[u];
  }
  while (depth[v] > depth[u]) {
    v = parent[v];
  }
  while (u != v) {
    u = parent[u];
    v = parent[v];
  }
  return u;
}
//*********************************
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cin >> V;
  rep(i, V) {
    int x;
    cin >> x;
    rep(j, x) {
      int y;
      cin >> y;
      edge[i].pb(y);
    }
  }
  init();
  int Q;
  cin >> Q;
  rep(i, Q) {
    int x, y;
    cin >> x >> y;
    cout << LCA(x, y) << endl;
  }
  return 0;
}