Sum integers

[shadowCODE]

I want to write a function bool possible(int sum, std::vector<int> &vec)
that checks for the possibility of summing the integers in vec to get sum without adding any number more than once.

e.g
vec = 140 80 90 180 70
sum = 300

Function returns true coz 140 + 90 + 70 == 300.

Can any one help with me how to go about this?

I wrote this but takes too long for large input.

bool possible(int sum, vector<int> &vec)
{
	do
	{
		int s = 0;
		for (int i = 0; i < vec.size(); i++)
		{
			s += vec.at(i);
			if (s == sum)
			{
				return true;
			}
				
		}
	}while(next_permutation(vec.begin(), vec.end()));

	return false;
}
}