sorry i forgot to attach.... here it is
On Sat, Dec 25, 2010 at 10:34 PM, Puneet Ginoria <[email protected]>wrote:
> This attachment contains the code for the above program in SML language and
> it uses lambda calculus.
>
>
> On Sat, Dec 25, 2010 at 9:18 PM, juver++ <[email protected]> wrote:
>
>> What you need to get for the answer - amount of such subsets or display
>> them?
>> First problem can be solved using DP.
>> Second - brute force.
>>
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fun depthfirst next pred x =
let
fun dfs([]) = []
| dfs(x::xs) =
if pred(x) then x::dfs(xs)
else dfs(next(x) @ xs)
in
dfs([x])
end;
fun sum([]) = 0 | sum(x::xs) = x + sum(xs);
fun check n ls = (sum(ls)=n);
fun last([]) = []
|last(x::xs) = if xs=[] then [x] else last(xs);
fun filt([],soln) = []
|filt(x::xs,soln) =
let
fun helper(x::xs,[y]) = if x=y then xs else
helper(xs,[y])
in
if last(soln) = [] then (x::xs) else
helper(x::xs,last(soln))
end;
fun listify(soln,[]) = []
|listify(soln,x::xs) = (op@(soln,[x]))::listify(soln,xs);
fun nextset ls soln = listify(soln,filt(ls,soln));
fun subset ls n = depthfirst (nextset ls) (check n) [];
