Problem p02658 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <assert.h>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(char x) { cerr << '\\'' << x << '\\''; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
void __print(const char *x) { cerr << '\\"' << x << '\\"'; }
void __print(const string &x) { cerr << '\\"' << x << '\\"'; }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifdef HOME
#warning CHECK int:ll::INT_MAX:LLONG_MAX
#define maxn 20
#define debug(x...)                                                            \\
  cerr << "[" << #x << "] = [";                                                \\
  _print(x)
#else
#define maxn 2000006
#define gcd __gcd
#define debug(x...)
#endif

#define ff first
#define endl '\\n'
#define ss second
#define inf 0x3f3f3f3f
#define MOD 1000000007
#define PI 3.14159265358979323846264338327950L
#define f(i, x, n) for (int i = x; i <= n; i++)
#define fr(i, x, n) for (int i = x; i >= n; i--)
struct _ {
  ios_base::Init i;
  _() { ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL); }
} _;

int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1};
int dy[] = {0, 1, 0, -1, -1, 1, 1, -1};

int main() {

  long long n;
  cin >> n;
  long long mul = 1;
  bool flg1 = false;
  bool flg2 = false;
  for (long long i = 1; i <= n; i++) {
    long long a;
    cin >> a;
    if (a == 0) {
      flg2 = true;
      break;
    }
    if (a > ((long long)1e18 / mul)) {
      flg1 = true;
    }
    if (flg1 == false)
      mul *= a;
  }

  if (flg1 == false and flg2 == false)
    cout << mul;
  else if (flg1 == true and flg2 == false)
    cout << -1;
  else if (flg1 == false and flg2 == true)
    cout << 0;
  else if (flg1 == true and flg2 == true)
    cout << 0;

  return 0;
}

Error: WA

Fixed submission:

#include <algorithm>
#include <assert.h>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(char x) { cerr << '\\'' << x << '\\''; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
void __print(const char *x) { cerr << '\\"' << x << '\\"'; }
void __print(const string &x) { cerr << '\\"' << x << '\\"'; }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifdef HOME
#warning CHECK int:ll::INT_MAX:LLONG_MAX
#define maxn 20
#define debug(x...)                                                            \\
  cerr << "[" << #x << "] = [";                                                \\
  _print(x)
#else
#define maxn 2000006
#define gcd __gcd
#define debug(x...)
#endif

#define ff first
#define endl '\\n'
#define ss second
#define inf 0x3f3f3f3f
#define MOD 1000000007
#define PI 3.14159265358979323846264338327950L
#define f(i, x, n) for (int i = x; i <= n; i++)
#define fr(i, x, n) for (int i = x; i >= n; i--)
struct _ {
  ios_base::Init i;
  _() { ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL); }
} _;

int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1};
int dy[] = {0, 1, 0, -1, -1, 1, 1, -1};

int main() {

  long long n;
  cin >> n;
  long long mul = 1;
  bool flg1 = false;
  bool flg2 = false;
  for (long long i = 1; i <= n; i++) {
    long long a;
    cin >> a;
    if (a == 0) {
      flg2 = true;
      break;
    }
    if (a > (1000000000000000000 / mul)) {
      flg1 = true;
    }
    mul *= a;
  }

  if (flg1 == false and flg2 == false)
    cout << mul;
  else if (flg1 == true and flg2 == false)
    cout << -1;
  else if (flg1 == false and flg2 == true)
    cout << 0;
  else if (flg1 == true and flg2 == true)
    cout << 0;

  return 0;
}