Subset Sum and Equal Partition

Given non-negative integers, can you split them into two groups with equal sums?

Implement:

• can_partition(nums)
• subset_with_sum(nums, target): a sorted list of indices whose values sum to target, or None. Any valid subset is fine.
• min_partition_difference(nums): the smallest possible |sum(A) - sum(B)| over all splits into two groups

Use the DP over reachable sums. A neat trick in Python: store the reachable set as the bits of one big integer, reach |= reach << x.