Problem p02558 (C++) — buggy submission, verdict: Runtime Error

#include "algorithm"
#include "bitset"
#include "cassert"
#include "climits"
#include "cmath"
#include "cstdio"
#include "ctime"
#include "functional"
#include "iomanip"
#include "iostream"
#include "list"
#include "map"
#include "numeric"
#include "queue"
#include "random"
#include "set"
#include "stack"
#include "string"
#include "unordered_map"
#include "unordered_set"

using namespace std;

constexpr long long int MOD = 1000000007;
// constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
// constexpr long long int MOD = 998244353;
constexpr double EPS = 1e-12;

// int N, M, K, T, H, W, L, R;
long long int N, M, K, T, H, W, L, R;

class UnionFind {
  vector<int> parent;
  vector<int> rank;

public:
  UnionFind(int num) {
    num++;
    parent.resize(num);
    rank.resize(num);
    for (int i = 0; i < num; i++) {
      parent[i] = i;
      rank[i] = 0;
    }
  }
  int Find(int node) {
    if (parent[node] == node)
      return node;
    else
      return parent[node] = Find(parent[node]);
  }
  void Unite(int u, int v) {
    u = Find(u);
    v = Find(v);
    if (u == v)
      return;
    if (rank[u] < rank[v])
      parent[u] = v;
    else {
      parent[v] = u;
      if (rank[u] == rank[v])
        rank[u]++;
    }
  }
  bool Check_Same(int u, int v) { return Find(u) == Find(v); }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  cin >> N >> K;
  UnionFind uf(N);
  while (K--) {
    int a, b, c;
    cin >> a >> b >> c;
    if (a) {
      cout << uf.Check_Same(b, c) << endl;
    } else {
      uf.Unite(b, c);
    }
  }
}

Error: WA

Fixed submission:

#include "algorithm"
#include "bitset"
#include "cassert"
#include "climits"
#include "cmath"
#include "cstdio"
#include "ctime"
#include "functional"
#include "iomanip"
#include "iostream"
#include "list"
#include "map"
#include "numeric"
#include "queue"
#include "random"
#include "set"
#include "stack"
#include "string"
#include "unordered_map"
#include "unordered_set"

using namespace std;

constexpr long long int MOD = 1000000007;
// constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
// constexpr long long int MOD = 998244353;
constexpr double EPS = 1e-12;

// int N, M, K, T, H, W, L, R;
long long int N, M, K, T, H, W, L, R;

class UnionFind {
  vector<int> parent;
  vector<int> rank;

public:
  UnionFind(int num) {
    num++;
    parent.resize(num);
    rank.resize(num);
    for (int i = 0; i < num; i++) {
      parent[i] = i;
      rank[i] = 0;
    }
  }
  int Find(int node) {
    if (parent[node] == node)
      return node;
    else
      return parent[node] = Find(parent[node]);
  }
  void Unite(int u, int v) {
    u = Find(u);
    v = Find(v);
    if (u == v)
      return;
    if (rank[u] < rank[v])
      parent[u] = v;
    else {
      parent[v] = u;
      if (rank[u] == rank[v])
        rank[u]++;
    }
  }
  bool Check_Same(int u, int v) { return Find(u) == Find(v); }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  cin >> N >> K;
  UnionFind uf(N);
  while (K--) {
    int a, b, c;
    cin >> a >> b >> c;
    b--, c--;
    if (a) {
      cout << uf.Check_Same(b, c) << endl;
    } else {
      uf.Unite(b, c);
    }
  }
}