网上的很多代码都是错的

正确的代码

using ll = long long int;
ll is_mul_overflow(ll a,ll b)
  {
  	if (a == -1)
  	  return (b == INT64_MIN);
  	if (b == -1)
  	  return (a == INT64_MIN);
  	if (a >= 0 and b >= 0)
  	  return a == 0 ? 0 : INT64_MAX / a < b;
	if(a < 0 and b < 0) 
	  return INT64_MAX / a > b;
	if (b < 0)
	  return INT64_MIN / b < a;
	else
	  return INT64_MIN / a < b;
  }