Problem p03045 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define rep(i, a) for (int i = 0; i < (a); i++)
typedef long long ll;

#ifdef _DEBUG
inline void dump() { cerr << endl; }
template <typename Head> void dump(Head &&head) {
  cerr << head;
  dump();
}
template <typename Head, typename... Tail>
void dump(Head &&head, Tail &&...tail) {
  cerr << head << ", ";
  dump(forward<Tail>(tail)...);
}
#define debug(...)                                                             \
  do {                                                                         \
    cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = ";                        \
    dump(__VA_ARGS__);                                                         \
  } while (false)
#else
#define dump(...)
#define debug(...)
#endif

template <typename T> struct edge {
  int src, to;
  T cost;
  edge(int to, T cost) : src(-1), to(to), cost(cost) {}
  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}
  edge &operator=(const int &x) {
    to = x;
    return *this;
  }
  operator int() const { return to; }
};
template <typename T> using Edges = vector<edge<T>>;
template <typename T> using WeightedGraph = vector<Edges<T>>;
using UnWeightedGraph = vector<vector<int>>;
template <typename T> using Matrix = vector<vector<T>>;

/////////////////////////////////////////////////////////////////////
const ll inf = 1LL << 60;

struct UnionFind {
  vector<int> data;
  UnionFind(int n) { init(n); }
  void init(int n = 1) { data.assign(n, -1); }
  int root(int x) {
    if (data[x] < 0)
      return x;
    return (data[x] = root(data[x]));
  }
  bool issame(int x, int y) { return (root(x) == root(y)); }
  bool merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (data[x] > data[y])
      swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return true;
  }
  int size(int x) { return (-data[root(x)]); }
};

int main() {
  ll n, m;
  cin >> n >> m;
  vector<ll> x(n);
  vector<ll> y(n);
  vector<ll> z(n);
  rep(i, m) {
    cin >> x[i] >> y[i] >> z[i];
    x[i]--;
    y[i]--;
    z[i] %= 2;
  }
  UnionFind uf(n);
  rep(i, m) { uf.merge(x[i], y[i]); }
  set<ll> st;
  rep(i, n) { st.insert(uf.root(i)); }
  cout << st.size() << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define rep(i, a) for (int i = 0; i < (a); i++)
typedef long long ll;

#ifdef _DEBUG
inline void dump() { cerr << endl; }
template <typename Head> void dump(Head &&head) {
  cerr << head;
  dump();
}
template <typename Head, typename... Tail>
void dump(Head &&head, Tail &&...tail) {
  cerr << head << ", ";
  dump(forward<Tail>(tail)...);
}
#define debug(...)                                                             \
  do {                                                                         \
    cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = ";                        \
    dump(__VA_ARGS__);                                                         \
  } while (false)
#else
#define dump(...)
#define debug(...)
#endif

template <typename T> struct edge {
  int src, to;
  T cost;
  edge(int to, T cost) : src(-1), to(to), cost(cost) {}
  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}
  edge &operator=(const int &x) {
    to = x;
    return *this;
  }
  operator int() const { return to; }
};
template <typename T> using Edges = vector<edge<T>>;
template <typename T> using WeightedGraph = vector<Edges<T>>;
using UnWeightedGraph = vector<vector<int>>;
template <typename T> using Matrix = vector<vector<T>>;

/////////////////////////////////////////////////////////////////////
const ll inf = 1LL << 60;

struct UnionFind {
  vector<int> data;
  UnionFind(int n) { init(n); }
  void init(int n = 1) { data.assign(n, -1); }
  int root(int x) {
    if (data[x] < 0)
      return x;
    return (data[x] = root(data[x]));
  }
  bool issame(int x, int y) { return (root(x) == root(y)); }
  bool merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (data[x] > data[y])
      swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return true;
  }
  int size(int x) { return (-data[root(x)]); }
};

int main() {
  ll n, m;
  cin >> n >> m;
  vector<ll> x(m);
  vector<ll> y(m);
  vector<ll> z(m);
  rep(i, m) {
    cin >> x[i] >> y[i] >> z[i];
    x[i]--;
    y[i]--;
    z[i] %= 2;
  }
  UnionFind uf(n);
  rep(i, m) { uf.merge(x[i], y[i]); }
  set<ll> st;
  rep(i, n) { st.insert(uf.root(i)); }
  cout << st.size() << endl;

  return 0;
}