string int2str(int num)
{
if (num == 0)
return " 0 ";
string str = "";
int num_ = num > 0 ? num : -1 * num;
while (num_)
{
str = (char) (num_ % 10 + 48) + str;
num_ /= 10;
}
if (num < 0)
str = " - " + str;
return str;
}