All Subsets that Add to a Value

Create a function that returns all sublists in a list that sum to a particular value. Return the sublists in the following order:

1. First by ascending length.
2. Second by comparing element-by-element, starting from the leftmost one. Put the list with the smaller element first in the pairwise comparison.

The following example will illustrate:

get_subsets([-3, -2, -1, 0, 1, 2, 3], 2)
[ # All the subsets below sum to 2.
  [2],
  [-1, 3],
  [0, 2], # Same length: -1 < 0, so [-1, 3] goes before [0, 2]
  [-3, 2, 3],
  [-2, 1, 3],
  [-1, 0, 3],
  [-1, 1, 2],
  [-3, 0, 2, 3],
  [-2, -1, 2, 3],
  [-2, 0, 1, 3], # Same length + same first element: -1 < 0, so [-2, -1, 2, 3] goes before [-2, 0, 1, 3]
  [-1, 0, 1, 2],
  [-3, -1, 1, 2, 3],
  [-2, -1, 0, 2, 3],
  [-3, -1, 0, 1, 2, 3]
]

Examples

get_subsets([-1, 0, 1, 2], 2) ➞ [[2], [0, 2], [-1, 1, 2], [-1, 0, 1, 2]]

get_subsets([-1, 0, 1, 2], 3) ➞ [[1, 2], [0, 1, 2]]

get_subsets([1, 2, 3, 4], 5) ➞ [[1, 4], [2, 3]]

get_subsets([-1, 0, 1, 2], 4) ➞ []

Notes

• Lists will have unique numbers.
• Return an empty list if there does not a exist a subset whose numbers sum to that value (see fourth example).