Quiz: Meet in the Middle

Subset Sum with $n = 40$ is infeasible with $O(2^n)$ brute force. How does meet-in-the-middle help?

1. A.It uses dynamic programming instead
2. B.It only considers subsets up to size $n/2$
3. C.It uses approximation
4. D.It splits into two $O(2^{20})$ searches and combines results