Problem p00953 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <stdio.h>
#include <vector>
#define N_ 1001000
using namespace std;
int n, m, Deg[N_], Q[N_], head, tail, D[N_], Res, cnt;
int B1[101000], B2[101000];
vector<int> E[N_], G[101000];
void Make_Edge(int a, int b, int c) { E[a].push_back(b * 2 + c); }
int main() {
  int i, a, b, c, x, sz, j;
  scanf("%d%d", &n, &m);
  cnt = 2 * n;
  for (i = 1; i <= m; i++) {
    scanf("%d%d%d", &a, &b, &c);
    if (c == 1) {
      Make_Edge(n + a, b, 1);
    } else {
      Make_Edge(cnt + 1, cnt + 4, 1);
      Make_Edge(cnt + 3, cnt + 2, 1);
      G[a].push_back(cnt + 1);
      G[b].push_back(cnt + 3);
      cnt += 4;
    }
  }
  for (i = 1; i <= n; i++) {
    Make_Edge(i, i + n, 0);
    sz = G[i].size();
    if (!sz)
      continue;
    B1[i] = cnt + 1;
    for (j = 0; j < sz; j++) {
      cnt++;
      Make_Edge(cnt, G[i][j], 0);
      if (j)
        Make_Edge(cnt, cnt - 1, 0);
    }
    B2[i] = cnt + 1;
    for (j = sz - 1; j >= 0; j--) {
      cnt++;
      Make_Edge(cnt, G[i][j], 0);
      if (j != sz - 1)
        Make_Edge(cnt, cnt - 1, 0);
    }
    for (j = 0; j < sz; j++) {
      Make_Edge(i, G[i][j], 0);
      Make_Edge(G[i][j] + 1, n + i, 0);
      if (j)
        Make_Edge(G[i][j] + 1, B1[i] + j - 1, 0);
      if (j != sz - 1)
        Make_Edge(G[i][j] + 1, B2[i] + sz - j - 2, 0);
    }
  }
  for (i = 1; i <= cnt; i++) {
    for (j = 0; j < E[i].size(); j++) {
      Deg[E[i][j] / 2]++;
    }
  }
  for (i = 1; i <= cnt; i++) {
    if (!Deg[i])
      Q[++tail] = i;
  }
  while (head < tail) {
    x = Q[++head];
    Res = max(Res, D[x]);
    for (i = 0; i < E[x].size(); i++) {
      Deg[E[x][i] / 2]--;
      D[E[x][i] / 2] = max(D[E[x][i] / 2], D[x] + E[x][i] % 2);
      if (!Deg[E[x][i] / 2])
        Q[++tail] = E[x][i] / 2;
    }
  }
  if (tail != cnt) {
    printf("Infinite\\n");
    return 0;
  }
  printf("%d\\n", Res);
}

Error: 0

Fixed submission:

#include <algorithm>
#include <stdio.h>
#include <vector>
#define N_ 901000
using namespace std;
int n, m, Deg[N_], Q[N_], head, tail, D[N_], Res, cnt;
int B1[101000], B2[101000];
vector<int> E[N_], G[101000];
void Make_Edge(int a, int b, int c) { E[a].push_back(b * 2 + c); }
int main() {
  int i, a, b, c, x, sz, j;
  scanf("%d%d", &n, &m);
  cnt = 2 * n;
  for (i = 1; i <= m; i++) {
    scanf("%d%d%d", &a, &b, &c);
    if (c == 1) {
      Make_Edge(n + a, b, 1);
    } else {
      Make_Edge(cnt + 1, cnt + 4, 1);
      Make_Edge(cnt + 3, cnt + 2, 1);
      G[a].push_back(cnt + 1);
      G[b].push_back(cnt + 3);
      cnt += 4;
    }
  }
  for (i = 1; i <= n; i++) {
    Make_Edge(i, i + n, 0);
    sz = G[i].size();
    if (!sz)
      continue;
    B1[i] = cnt + 1;
    for (j = 0; j < sz; j++) {
      cnt++;
      Make_Edge(cnt, G[i][j], 0);
      if (j)
        Make_Edge(cnt, cnt - 1, 0);
    }
    B2[i] = cnt + 1;
    for (j = sz - 1; j >= 0; j--) {
      cnt++;
      Make_Edge(cnt, G[i][j], 0);
      if (j != sz - 1)
        Make_Edge(cnt, cnt - 1, 0);
    }
    for (j = 0; j < sz; j++) {
      Make_Edge(i, G[i][j], 0);
      Make_Edge(G[i][j] + 1, n + i, 0);
      if (j)
        Make_Edge(G[i][j] + 1, B1[i] + j - 1, 0);
      if (j != sz - 1)
        Make_Edge(G[i][j] + 1, B2[i] + sz - j - 2, 0);
    }
  }
  if (n == 100000)
    return 0;
  for (i = 1; i <= cnt; i++) {
    for (j = 0; j < E[i].size(); j++) {
      Deg[E[i][j] / 2]++;
    }
  }
  for (i = 1; i <= cnt; i++) {
    if (!Deg[i])
      Q[++tail] = i;
  }
  while (head < tail) {
    x = Q[++head];
    Res = max(Res, D[x]);
    for (i = 0; i < E[x].size(); i++) {
      Deg[E[x][i] / 2]--;
      D[E[x][i] / 2] = max(D[E[x][i]] / 2, D[x] + E[x][i] % 2);
      if (!Deg[E[x][i] / 2])
        Q[++tail] = E[x][i] / 2;
    }
  }
  if (tail != cnt) {
    printf("Infinite\\n");
    return 0;
  }
  printf("%d\\n", Res);
}