Problem p02558 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

const double pi = 3.141592653589793238462643383279;
using namespace std;

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<long long, long long> PLL;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

// container util
//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SQ(a) ((a) * (a))
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define MOD 1000000007

#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define trav(a, x) for (auto &a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
const long double EPS = 1e-6, PI = acos((long double)-1);

// ここから編集
struct UnionFind {
  vector<int> par;
  vector<int> siz;

  UnionFind(int sz_) : par(sz_), siz(sz_) {
    for (int i = 0; i < sz_; ++i)
      par[i] = i, siz[i] = 1;
  }

  void init(int sz_) {
    par.resize(sz_);
    siz.resize(sz_);
    for (int i = 0; i < sz_; ++i)
      par[i] = i, siz[i] = 1;
  }

  int root(int x) {
    if (x == par[x])
      return x;
    return par[x] = root(par[x]);
  }

  bool merge(int x, int y) {
    x = root(x), y = root(y);
    if (x == y)
      return false;
    if (siz[x] < siz[y])
      swap(x, y);
    siz[x] += siz[y];
    par[y] = x;
    return true;
  }

  bool issame(int x, int y) { return root(x) == root(y); }

  int size(int x) { return siz[root(x)]; }
};
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(4);

  int N, Q;
  cin >> N >> Q;
  UnionFind uf(N);
  REP(i, Q) {
    int t, u, v;
    cin >> t >> u >> v;
    u--;
    v--;
    if (t == 0) {
      uf.merge(u, v);
    } else {
      if (uf.issame(u, v)) {
        cout << 1 << endl;
      } else {
        cout << 0 << endl;
      }
    }
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>

const double pi = 3.141592653589793238462643383279;
using namespace std;

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<long long, long long> PLL;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

// container util
//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SQ(a) ((a) * (a))
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define MOD 1000000007

#define rep(i, a, b) for (int i = a; i < (b); ++i)
#define trav(a, x) for (auto &a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
const long double EPS = 1e-6, PI = acos((long double)-1);

// ここから編集
struct UnionFind {
  vector<int> par;
  vector<int> siz;

  UnionFind(int sz_) : par(sz_), siz(sz_) {
    for (int i = 0; i < sz_; ++i)
      par[i] = i, siz[i] = 1;
  }

  void init(int sz_) {
    par.resize(sz_);
    siz.resize(sz_);
    for (int i = 0; i < sz_; ++i)
      par[i] = i, siz[i] = 1;
  }

  int root(int x) {
    if (x == par[x])
      return x;
    return par[x] = root(par[x]);
  }

  bool merge(int x, int y) {
    x = root(x), y = root(y);
    if (x == y)
      return false;
    if (siz[x] < siz[y])
      swap(x, y);
    siz[x] += siz[y];
    par[y] = x;
    return true;
  }

  bool issame(int x, int y) { return root(x) == root(y); }

  int size(int x) { return siz[root(x)]; }
};
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(4);

  int N, Q;
  cin >> N >> Q;
  UnionFind uf(N);
  REP(i, Q) {
    int t, u, v;
    cin >> t >> u >> v;

    if (t == 0) {
      uf.merge(u, v);
    } else {
      if (uf.issame(u, v)) {
        cout << 1 << endl;
      } else {
        cout << 0 << endl;
      }
    }
  }
  return 0;
}