Problem p00316 (C++) — buggy submission, verdict: Runtime Error

#include <cstdio>
#include <iostream>
#include <vector>
#define _USE_MATH_DEFINES
#include <algorithm>
#include <array>
#include <chrono>
#include <complex>
#include <cstring>
#include <functional>
#include <limits.h>
#include <map>
#include <math.h>
#include <nmmintrin.h>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <stdlib.h>
#include <string>
#include <unordered_map>
#define rep(i, s, n) for (int i = (s); (n) > i; i++)
#define REP(i, n) rep(i, 0, n)
#define RANGE(x, a, b) ((a) <= (x) && (x) <= (b))
#define DUPLE(a, b, c, d)                                                      \\
  (RANGE(a, c, d) || RANGE(b, c, d) || RANGE(c, a, b) || RANGE(d, a, b))
#define INCLU(a, b, c, d) (RANGE(a, c, d) && (b, c, d))
#define PW(x) ((x) * (x))
#define ALL(x) (x).begin(), (x).end()
#define MODU 1000000007
#define bitcheck(a, b) ((a >> b) & 1)
#define bitset(a, b) (a |= (1 << b))
#define bitunset(a, b) (a &= ~(1 << b))
#define MP(a, b) make_pair((a), (b))
#define Manh(a, b) (abs((a).first-(b).first) + abs((a).second - ((b).second))
#define pritnf printf
#define scnaf scanf
#define itn int
#ifdef _MSC_VER
#define __builtin_popcount _mm_popcnt_u32
#define __builtin_popcountll _mm_popcnt_u64
#endif
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

struct UnionFind {
  vector<int> data;
  int n, m;

  UnionFind(int ns, int ms) : n(ns), m(ms), data(ns + ms, INT_MIN) {
    REP(i, m) { data[i + n] = -i - 1; }
  }

  bool unite(int a, int b) { // 矛盾の判定
    a = root(a), b = root(b);

    if (a == b)
      return true;

    if (data[a] != INT_MIN && data[b] != INT_MIN) {
      if (data[a] != data[b]) {
        return false;
      } else {
        if (rand() % 2)
          data[b] = a;
        else
          data[a] = b;
      }
    } else if (data[a] != INT_MIN)
      data[b] = a;
    else if (data[b] != INT_MIN)
      data[a] = b;
    else {
      if (rand() % 2)
        data[b] = a;
      else
        data[a] = b;
    }
    return true;
  }

  bool unitebu(int a, int b) { // 矛盾の判定 aをbの部活
    a = root(a);
    b += n;

    if (data[a] == data[b])
      return true;
    if (data[a] != INT_MIN)
      return false;

    data[a] = b;
    return true;
  }

  bool findset(int a, int b) { return root(a) == root(b); }

  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
};

signed main() {
  int n, m, k;
  cin >> n >> m >> k;
  UnionFind uf(n, m);
  REP(i, k) {
    int t, a, b;
    scanf("%d %d %d", &t, &a, &b);
    bool ret = 1;
    a--, b--;
    if (t == 1) {
      ret = uf.unite(a, b);
    } else if (t == 2) {
      ret = uf.unitebu(a, b);
    }

    if (!ret) {
      printf("%d\\n", i + 1);
      return 0;
    }
  }

  printf("0\\n");

  return 0;
}

Error: 0

Fixed submission:

#include <cstdio>
#include <iostream>
#include <vector>
#define _USE_MATH_DEFINES
#include <algorithm>
#include <array>
#include <chrono>
#include <complex>
#include <cstring>
#include <functional>
#include <limits.h>
#include <map>
#include <math.h>
#include <nmmintrin.h>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <stdlib.h>
#include <string>
#include <unordered_map>
#define rep(i, s, n) for (int i = (s); (n) > i; i++)
#define REP(i, n) rep(i, 0, n)
#define RANGE(x, a, b) ((a) <= (x) && (x) <= (b))
#define DUPLE(a, b, c, d)                                                      \\
  (RANGE(a, c, d) || RANGE(b, c, d) || RANGE(c, a, b) || RANGE(d, a, b))
#define INCLU(a, b, c, d) (RANGE(a, c, d) && (b, c, d))
#define PW(x) ((x) * (x))
#define ALL(x) (x).begin(), (x).end()
#define MODU 1000000007
#define bitcheck(a, b) ((a >> b) & 1)
#define bitset(a, b) (a |= (1 << b))
#define bitunset(a, b) (a &= ~(1 << b))
#define MP(a, b) make_pair((a), (b))
#define Manh(a, b) (abs((a).first-(b).first) + abs((a).second - ((b).second))
#define pritnf printf
#define scnaf scanf
#define itn int
#ifdef _MSC_VER
#define __builtin_popcount _mm_popcnt_u32
#define __builtin_popcountll _mm_popcnt_u64
#endif
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

struct UnionFind {
  vector<int> data;
  int n, m;

  UnionFind(int ns, int ms) : n(ns), m(ms), data(ns + ms, INT_MIN) {
    REP(i, m) { data[i + n] = -i - 1; }
  }

  bool unite(int a, int b) { // 矛盾の判定
    a = root(a), b = root(b);

    if (data[a] != INT_MIN && data[b] != INT_MIN) {
      if (data[a] != data[b]) {
        return false;
      } else {
        if (rand() % 2)
          data[b] = a;
        else
          data[a] = b;
      }
    } else if (data[a] != INT_MIN)
      data[b] = a;
    else if (data[b] != INT_MIN)
      data[a] = b;
    else {
      if (rand() % 2)
        data[b] = a;
      else
        data[a] = b;
    }
    return true;
  }

  bool unitebu(int a, int b) { // 矛盾の判定 aをbの部活
    a = root(a);
    b += n;

    if (data[a] == data[b])
      return true;
    if (data[a] != INT_MIN)
      return false;

    data[a] = b;
    return true;
  }

  bool findset(int a, int b) { return root(a) == root(b); }

  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }

  int getbu(int x) { return data[root(x)] == INT_MIN ? INT_MAX : data[x] - n; }
};

signed main() {
  int n, m, k;
  cin >> n >> m >> k;
  UnionFind uf(n, m);
  REP(i, k) {
    int t, a, b;
    scanf("%d %d %d", &t, &a, &b);
    bool ret = 1;
    a--, b--;
    if (t == 1) {
      ret = uf.unite(a, b);
    } else if (t == 2) {
      ret = uf.unitebu(a, b);
    }

    if (!ret) {
      printf("%d\\n", i + 1);
      return 0;
    }
  }

  printf("0\\n");

  return 0;
}