Subset sum problem

The subset sum problem is an important problem of computer science. It can be stated as follows: Given a set of integers, does any subset of them sum to zero? For example, given the set { -7, -3, -2, 5, 8}, the answer is "yes" because the subset { -3, -2, 5} sums to zero. The problem is NP-Complete. It can be reformulated to the 3SAT. 
An alternative statement of this problem is, given a set of numbers and an integer x determine whether or not there exist a subset that sums up to x.
Eg. given a set {1, 4, 6, 7} and x = 10 the answer is "yes" because {4, 6} sums to 10. 
Remember that the subsequence need not to be contiguous. For instance if x = 8 in above example the answer is still yes because {1, 7} sums to 8.