HackerEarth Two paths problem solution

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <cmath>
#include <ctime>
#include <functional>
#include <sstream>
#include <fstream>
#include <valarray>
#include <complex>
#include <queue>
#include <cassert>
#include <bitset>
using namespace std;

#ifdef LOCAL
#define debug_flag 0
#else
#define debug_flag 0
#endif

  template <class T1, class T2 >
std::ostream& operator << (std::ostream& os, const pair<T1, T2> &p) 
{
  os << "[" << p.first << ", " << p.second << "]";
  return os;
}

  template <class T >
std::ostream& operator << (std::ostream& os, const std::vector<T>& v) 
{
  os << "[";
  bool first = true;
  for (typename std::vector<T>::const_iterator it = v.begin(); it != v.end(); ++it)
  {
    if (!first)
      os << ", ";
    first = false;
    os << *it;
  }
  os << "]";
  return os;
}

#define dbg(args...) { if (debug_flag) { _print(_split(#args, ',').begin(), args); cerr << endl; } else { void(0);} }

vector<string> _split(const string& s, char c) {
  vector<string> v;
  stringstream ss(s);
  string x;
  while (getline(ss, x, c))
    v.emplace_back(x);
  return v;
}

void _print(vector<string>::iterator) {}
template<typename T, typename... Args>
void _print(vector<string>::iterator it, T a, Args... args) {
  string name = it -> substr((*it)[0] == ' ', it -> length());
  if (isalpha(name[0]))
    cerr << name  << " = " << a << " ";
  else
    cerr << name << " ";
  _print(++it, args...);
}

typedef long long int int64;

const int N = (int)4e5 + 1000;
const int LOGN = 20;

int n, m, q;
vector<int> graph[N];
vector<pair<int, int> > black_edges;

int white_comp_cnt;
int v_to_white_comp[N];

int timer;
int t_in[N], t_out[N];
int f_up[N];
bool is_articulation_point[N];

int block_cnt;
int block_id[N];
vector<int> cur_block;

vector<int> block_graph[N];
int par[N][LOGN];

bool used[N];

int black_color[N];

vector<vector<int> > blocks;

void dfs_comp(int v)
{
  v_to_white_comp[v] = white_comp_cnt;
  for (int to : graph[v])
    if (v_to_white_comp[to] == -1)
      dfs_comp(to);
}

void proccess_block(int limit_size)
{
  vector<int> cur_comp;
  while ((int)cur_block.size() > limit_size)
  {
    cur_comp.push_back(cur_block.back());
    cur_block.pop_back();
  }

  blocks.push_back(cur_comp);
}

void init_dfs(int v, int p, int cur_black_color)
{
  //dbg(v, p);

  black_color[v] = cur_black_color;

  cur_block.push_back(v);

  t_in[v] = f_up[v] = timer++;

  used[v] = true;

  int to_cnt = 0;

  for (int to : graph[v])
  {
    if (to == p)
      continue;

    if (used[to])
    {
      f_up[v] = min(f_up[v], t_in[to]);
    }
    else
    {
      int limit_size = (int)cur_block.size();

      to_cnt++;
      init_dfs(to, v, cur_black_color);

      if (f_up[to] >= t_in[v])
      {
        if (p != -1 || (p == -1 && to_cnt > 1))
        {
          proccess_block(limit_size);
          blocks.back().push_back(v);
        }

        if (p != -1)
          is_articulation_point[v] = true;
      }

      f_up[v] = min(f_up[v], f_up[to]);
    }
  }

  if (p == -1)
    is_articulation_point[v] = (to_cnt > 1);
}

bool is_par(int p, int v)
{
  return t_in[p] <= t_in[v] && t_out[v] <= t_out[p];
}

int get_lca(int a, int b)
{
  if (is_par(a, b))
    return a;

  if (is_par(b, a))
    return b;

  for (int i = LOGN - 1; i >= 0; i--)
  {
    int new_a = par[a][i];
    if (new_a == -1 || is_par(new_a, b))
      continue;
    a = new_a;
  }

  return par[a][0];
}

void block_dfs(int v, int p)
{
  t_in[v] = timer++;

  used[v] = true;

  par[v][0] = p;
  for (int i = 1; i < LOGN; i++)
  {
    if (par[v][i - 1] == -1)
      break;
    par[v][i] = par[par[v][i - 1]][i - 1];
  }

  for (int to : block_graph[v])
  {
    if (used[to])
      continue;
    block_dfs(to, v);
  }

  t_out[v] = timer++;
}

void init_graph()
{
  fill(v_to_white_comp, v_to_white_comp + n, -1);
  for (int i = 0; i < n; i++)
  {
    if (v_to_white_comp[i] != -1)
      continue;
    dfs_comp(i);
    white_comp_cnt++;
  }

  //for (int i = 0; i < n; i++)
  //dbg(i, v_to_white_comp[i]);

  for (int i = 0; i < n; i++)
    graph[i].clear();

  for (auto p : black_edges)
  {
    int a = p.first;
    int b = p.second;

    a = v_to_white_comp[a];
    b = v_to_white_comp[b];

    if (a != b)
    {
      //dbg("black", a, b);
      graph[a].push_back(b);
      graph[b].push_back(a);
    }
  }

  fill(used, used + white_comp_cnt, false);

  int black_cnt = 0;

  fill(block_id, block_id + n, -1);

  for (int i = 0; i < white_comp_cnt; i++)
  {
    if (used[i])
      continue;

    init_dfs(i, -1, black_cnt);
    black_cnt++;

    proccess_block(0);
  }

  dbg(blocks);

  for (int i = 0; i < white_comp_cnt; i++)
    dbg(i, is_articulation_point[i]);

  block_cnt = (int)blocks.size() + white_comp_cnt;

  dbg(block_cnt);

  for (int i = 0; i < (int)blocks.size(); i++)
  {
    for (int v : blocks[i])
    {
      block_id[v] = i;

      if (is_articulation_point[v])
      {
        int a = i;
        int b = v + (int)blocks.size();

        dbg("block edge", a, b);

        block_graph[a].push_back(b);
        block_graph[b].push_back(a);
      }
    }
  }

  fill(used, used + block_cnt, false);

  for (int i = 0; i < block_cnt; i++)
    for (int j = 0; j < LOGN; j++)
      par[i][j] = -1;

  for (int i = 0; i < block_cnt; i++)
  {
    if (used[i])
      continue;

    block_dfs(i, -1);
  }

  //for (int i = 0; i < white_comp_cnt; i++)
  //dbg(i, is_articulation_point[i]);
}

bool on_path(int v, int a, int b)
{
  return is_par(b, v) && is_par(v, a);
}

bool check(int a, int b, int c)
{
  dbg("check", a, b, c);
  //a != b holds

  if (c == a || c == b)
    return false;

  if (!is_articulation_point[c])
    return true;

  if (is_articulation_point[a])
    a = (int)blocks.size() + a;
  else
    a = block_id[a];

  if (is_articulation_point[b])
    b = (int)blocks.size() + b;
  else
    b = block_id[b];

  c = (int)blocks.size() + c;

  int lca = get_lca(a, b);

  dbg(a, b, c, lca);

  if (on_path(c, a, lca) || on_path(c, b, lca))
    return false;

  return true;
}

bool solve(int a, int b, int c, int d)
{
  a = v_to_white_comp[a];
  b = v_to_white_comp[b];
  c = v_to_white_comp[c];
  d = v_to_white_comp[d];

  //dbg(a, b, c, d);

  if (black_color[a] != black_color[b])
    return false;

  if (black_color[c] != black_color[d])
    return true;

  if (c == d)
    return false;

  if (a == b)
    return true;

  if (check(a, b, c))
    return true;

  if (check(a, b, d))
    return true;

  return false;
}

int main()
{
#ifdef LOCAL
  freopen ("input.txt", "r", stdin);
#endif

  scanf("%d%d%d", &n, &m, &q);

  for (int i = 0; i < m; i++)
  {
    int a, b, t;
    scanf("%d%d%d", &a, &b, &t);
    a--;
    b--;

    dbg(a, b, t);

    if (t == 0)
      black_edges.emplace_back(a, b);
    else
    {
      graph[a].push_back(b);
      graph[b].push_back(a);
    }
  }

  init_graph();

  for (int i = 0; i < q; i++)
  {
    int a, b, c, d;
    scanf("%d%d%d%d", &a, &b, &c, &d);
    a--;
    b--;
    c--;
    d--;

    dbg(a, b, c, d);

    bool res = solve(a, b, c, d);
    printf("%sn", res ? "Yes" : "No");
  }

  return 0;
}