Problem p02373 (C++) — buggy submission, verdict: Runtime Error

#include "bits/stdc++.h"
#include <fstream>
#include <sys/timeb.h>

using namespace std;

#define repr(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) repr(i, 0, n)
#define reprrev(i, a, b) for (int i = (int)(b)-1; i >= (int)(a); i--)
#define reprev(i, n) reprrev(i, 0, n)
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define exist(container, item)                                                 \\
  (lower_bound(container.begin(), container.end(), item) != container.end())
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define mp make_pair
#define mt make_tuple
#define INF 1050000000
#define INFL 9e18
#define EPS (1e-10)
#define MOD 1000000007
#define PI 3.1415926536
#define RMAX 4294967295

typedef long long ll;
typedef pair<int, int> Pi;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<Pi> vPi;
typedef vector<vector<int>> vvi;
typedef vector<vector<bool>> vvb;
typedef vector<vector<ll>> vvll;
typedef vector<vector<char>> vvc;
typedef vector<vector<string>> vvs;
typedef vector<vector<double>> vvd;
typedef vector<vector<Pi>> vvPi;
typedef priority_queue<int, vector<int>, greater<int>> pqli;
typedef priority_queue<ll, vector<ll>, greater<ll>> pqlll;
typedef priority_queue<Pi, vector<Pi>, greater<Pi>> pqlP;
struct Edge {
  int from, to, cost;
  bool operator<(Edge e) { return cost < e.cost; }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
template <class T> using vec = vector<T>;
template <class T> using pql = priority_queue<T, vector<T>, greater<T>>;
string debug_show(Pi a) {
  return "(" + to_string(a.first) + "," + to_string(a.second) + ")";
}

template <class T> struct augEdge {
  T from, to;
  int cost;
  bool operator<(augEdge e) { return cost < e.cost; }
  bool operator>(augEdge e) { return cost > e.cost; }
};
template <class T> using augGraph = vector<augEdge<T>>;

class LCA {
public:
  int N;
  vi depth;
  int maxdepth = 0;
  vvi dblpar;

  LCA(const Graph G) {
    N = G.size();
    depth = vi(N);
    dfs1(G, 0, -1);
    int D = bindigit(maxdepth) + 1;
    dblpar = vvi(D, vi(N));
    rep(i, D) { dfs2(G, 0, 0, i); }
  }

  void dfs1(const Graph &G, int pos, int par, int d = 0) {
    depth[pos] = d;
    maxdepth = max(maxdepth, d);
    for (auto e : G[pos]) {
      if (e.to == par)
        continue;
      dfs1(G, e.to, pos, d + 1);
    }
  }

  void dfs2(const Graph &G, int pos, int par, int dbl) {
    if (dbl == 0) {
      dblpar[0][pos] = par;
    } else {
      dblpar[dbl][pos] = dblpar[dbl - 1][dblpar[dbl - 1][pos]];
    }
    for (auto e : G[pos]) {
      if (e.to == par)
        continue;
      dfs2(G, e.to, pos, dbl);
    }
  }

  int parent(int pos, int step) {
    int ret = pos;
    int dbl = 0;
    while (step > 0) {
      if ((step & 1) != 0) {
        ret = dblpar[dbl][ret];
      }
      step >>= 1;
      dbl++;
    }
    return ret;
  }

  int bindigit(int n) {
    int ret = 0;
    while (n > 0) {
      ret++;
      n >>= 1;
    }
    return ret;
  }

  int lca(int u, int v) {
    if (depth[u] < depth[v]) {
      swap(u, v);
    }
    u = parent(u, depth[u] - depth[v]);
    int ng = -1, ok = depth[u];
    while (ok - ng > 1) {
      int mid = (ok + ng) / 2;
      if (parent(u, mid) == parent(v, mid)) {
        ok = mid;
      } else {
        ng = mid;
      }
    }
    return parent(u, ok);
  }
};

int main(void) {
  int N;
  cin >> N;
  Graph G(N);
  rep(i, N) {
    int num;
    cin >> num;
    rep(j, num) {
      int ch;
      cin >> ch;
      G[i].push_back(Edge{i, ch, 1});
      G[ch].push_back(Edge{ch, i, 1});
    }
  }

  LCA lca(G);

  int Q;
  cin >> Q;
  rep(q, Q) {
    int u, v;
    cin >> u >> v;
    cout << lca.lca(u, v) << endl;
  }

  return 0;
}

Error: -11

Fixed submission:

#include "bits/stdc++.h"
#include <fstream>
#include <sys/timeb.h>

using namespace std;

#define repr(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) repr(i, 0, n)
#define reprrev(i, a, b) for (int i = (int)(b)-1; i >= (int)(a); i--)
#define reprev(i, n) reprrev(i, 0, n)
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define exist(container, item)                                                 \\
  (find(container.begin(), container.end(), item) != container.end())
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define mp make_pair
#define mt make_tuple
#define INF 1050000000
#define INFL 9e18
#define EPS (1e-10)
#define MOD 1000000007
#define PI 3.1415926536
#define RMAX 4294967295

typedef long long ll;
typedef pair<int, int> Pi;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<Pi> vPi;
typedef vector<vector<int>> vvi;
typedef vector<vector<bool>> vvb;
typedef vector<vector<ll>> vvll;
typedef vector<vector<char>> vvc;
typedef vector<vector<string>> vvs;
typedef vector<vector<double>> vvd;
typedef vector<vector<Pi>> vvPi;
typedef priority_queue<int, vector<int>, greater<int>> pqli;
typedef priority_queue<ll, vector<ll>, greater<ll>> pqlll;
typedef priority_queue<Pi, vector<Pi>, greater<Pi>> pqlP;
struct Edge {
  int from, to, cost;
  bool operator<(Edge e) { return cost < e.cost; }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
template <class T> using vec = vector<T>;
template <class T> using pql = priority_queue<T, vector<T>, greater<T>>;
string debug_show(Pi a) {
  return "(" + to_string(a.first) + "," + to_string(a.second) + ")";
}

template <class T> struct augEdge {
  T from, to;
  int cost;
  bool operator<(augEdge e) { return cost < e.cost; }
  bool operator>(augEdge e) { return cost > e.cost; }
};
template <class T> using augGraph = vector<augEdge<T>>;

class LCA {
public:
  int N;
  vi depth;
  int maxdepth = 0;
  vvi dblpar;

  LCA(const Graph G) {
    N = G.size();
    depth = vi(N);
    dfs1(G, 0);
    int D = bindigit(maxdepth) + 1;
    dblpar = vvi(D, vi(N));
    rep(i, D) { dfs2(G, 0, 0, i); }
  }

  void dfs1(const Graph &G, int pos, int d = 0) {
    depth[pos] = d;
    maxdepth = max(maxdepth, d);
    for (auto ch : G[pos]) {
      dfs1(G, ch.to, d + 1);
    }
  }

  void dfs2(const Graph &G, int pos, int par, int dbl) {
    if (dbl == 0) {
      dblpar[0][pos] = par;
    } else {
      dblpar[dbl][pos] = dblpar[dbl - 1][dblpar[dbl - 1][pos]];
    }
    for (auto ch : G[pos]) {
      dfs2(G, ch.to, pos, dbl);
    }
  }

  int parent(int pos, int step) {
    int ret = pos;
    int dbl = 0;
    while (step > 0) {
      if ((step & 1) != 0) {
        ret = dblpar[dbl][ret];
      }
      step >>= 1;
      dbl++;
    }
    return ret;
  }

  int bindigit(int n) {
    int ret = 0;
    while (n > 0) {
      ret++;
      n >>= 1;
    }
    return ret;
  }

  int lca(int u, int v) {
    if (depth[u] < depth[v]) {
      swap(u, v);
    }
    u = parent(u, depth[u] - depth[v]);
    int ng = -1, ok = depth[u];
    while (ok - ng > 1) {
      int mid = (ok + ng) / 2;
      if (parent(u, mid) == parent(v, mid)) {
        ok = mid;
      } else {
        ng = mid;
      }
    }
    return parent(u, ok);
  }
};

int main(void) {
  int N;
  cin >> N;
  Graph G(N);
  rep(i, N) {
    int num;
    cin >> num;
    rep(j, num) {
      int ch;
      cin >> ch;
      G[i].push_back(Edge{i, ch, 1});
      G[ch].push_back(Edge{ch, i, 1});
    }
  }

  LCA lca(G);

  int Q;
  cin >> Q;
  rep(q, Q) {
    int u, v;
    cin >> u >> v;
    cout << lca.lca(u, v) << endl;
  }

  return 0;
}