HackerEarth Furthest vertex problem solution

In this HackerEarth Furthest vertex problem solution There are n vertices.

Your task is to perform q queries:

1 a b – add an undirected edge of the length 1 between vertices a and b

2 a – find the distance to the furthest vertex reachable from the vertex a

Guaranteed that graph will not contain loops and cycles during all the time.

#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 1
#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;

struct Query
{
  int type, a, b;
  Query() : type(), a(), b() {}
  Query(int _type, int _a, int _b) : type(_type), a(_a), b(_b) {}
};

const int N = (int)1e5 + 100;
const int Q = (int)3e5 + 100;
const int LOGN = 18;

const int ADD_EDGE = 1;

struct DSU
{
  int par[N];

  DSU()
  {
    init();
  }

  void init()
  {
    for (int i = 0; i < N; i++)
      par[i] = i;
  }

  int get_id(int a)
  {
    if (par[a] == a)
      return a;
    return par[a] = get_id(par[a]);
  }

  bool join(int a, int b)
  {
    a = get_id(a);
    b = get_id(b);
    if (a == b)
      return false;
    par[a] = b;
    return true;
  }
};

int n, q;
vector<int> graph[N];
Query q_list[Q];

bool used[N];
int h[N];
int par[N][LOGN];

int d1[N], d2[N];

void dfs(int v, int p, int cur_h)
{
  used[v] = true;

  h[v] = cur_h;

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

    dfs(to, v, cur_h + 1);
  }
}

int get_lca(int a, int b)
{
  if (h[a] < h[b])
    swap(a, b);

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

  if (a == b)
    return a;

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

  return par[a][0];
}

int get_dist(int a, int b)
{
  int l = get_lca(a, b);
  return h[a] + h[b] - 2 * h[l];
}

void precalc()
{
  for (int i = 0; i < q; i++)
  {
    if (q_list[i].type != ADD_EDGE)
      continue;
    int a = q_list[i].a;
    int b = q_list[i].b;
    graph[a].push_back(b);
    graph[b].push_back(a);
  }

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

  for (int i = 0; i < n; i++)
  {
    if (used[i])
      continue;
    dfs(i, -1, 0);
  }

  for (int i = 0; i < n; i++)
    d1[i] = d2[i] = i;
}

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

  scanf("%d%d", &n, &q);
  for (int i = 0; i < q; i++)
  {
    int type;
    scanf("%d", &type);

    if (type == ADD_EDGE)
    {
      int a, b;
      scanf("%d%d", &a, &b);
      a--;
      b--;
      q_list[i] = Query(type, a, b);
    }
    else
    {
      int a;
      scanf("%d", &a);
      a--;
      q_list[i] = Query(type, a, -1);
    }
  }

  precalc();

  DSU dsu = DSU();

  for (int i = 0; i < q; i++)
  {
    if (q_list[i].type == ADD_EDGE)
    {
      int a = q_list[i].a;
      int b = q_list[i].b;
      int a_id = dsu.get_id(a);
      int b_id = dsu.get_id(b);

      int c1 = d1[a_id];
      int c2 = d2[a_id];
      int c3 = d1[b_id];
      int c4 = d2[b_id];

      assert(dsu.join(a, b));

      int new_a = c2;
      if (get_dist(c1, new_a) < get_dist(c1, c3))
        new_a = c3;
      if (get_dist(c1, new_a) < get_dist(c1, c4))
        new_a = c4;

      int new_b = c1;
      if (get_dist(new_a, new_b) < get_dist(new_a, c2))
        new_b = c2;
      if (get_dist(new_a, new_b) < get_dist(new_a, c3))
        new_b = c3;
      if (get_dist(new_a, new_b) < get_dist(new_a, c4))
        new_b = c4;

      int id = dsu.get_id(a);
      d1[id] = new_a;
      d2[id] = new_b;
    }
    else
    {
      int a = q_list[i].a;
      int a_id = dsu.get_id(a);
      int dist1 = get_dist(a, d1[a_id]);
      int dist2 = get_dist(a, d2[a_id]);
      int ans = max(dist1, dist2);
      printf("%dn", ans);
    }
  }

  return 0;
}