However neither of those solutions actualy get what the poster asked for unless i'm misunderstanding your explanation.

2 3 5 10 20
target  = 29
asc     = 2 3 5 10 = 18 distance = 11
desc    = 20 5 3   = 28 distance =  2
closest = 20 10    = 30 distance =  1

2 3 4 5 10 20
target  = 40
asc     = 2 3 4 5 10  = 24 distance = 16
desc    = 20 10 5 4   = 39 distance =  1
closest = 20 10 5 3 2 = 40 distance =  0
[download]

In both cases that algorithm failes to get the closes match. I don't have a solution so I should probably shut up, but I was curious if i missed something in your explanation, of if that is just solving a similar problem.