20 lines
1.2 KiB
FSharp
20 lines
1.2 KiB
FSharp
(*
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Encode and Decode using StraddlingCheckerboard
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Nigel Galloway May 15th., 2017
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*)
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type G={n:char;i:char;g:System.Collections.Generic.Dictionary<(char*char),string>;e:System.Collections.Generic.Dictionary<char,string>}
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member G.encode n=n|>Seq.map(fun n->if (n='/') then G.e.['/']+string n else match (G.e.TryGetValue(n)) with |(true,n)->n|(false,_)->G.e.['/']+string n)
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member G.decode n =
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let rec fn n = seq{ if not (Seq.isEmpty n)
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then match (match Seq.head n with |g when g=G.n||g=G.i->(G.g.[(g,(Seq.item 1 n))],(Seq.skip 2 n))|g->(G.g.[('/',g)],(Seq.tail n))) with
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|(a,b) when a="/"->yield string (Seq.head b); yield! fn (Seq.tail b)
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|(a,b) ->yield a; yield! fn b
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}
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fn n
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let G n i g e l z=
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let a = new System.Collections.Generic.Dictionary<(char*char),string>()
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let b = new System.Collections.Generic.Dictionary<char,string>()
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Seq.iter2 (fun ng gn->a.[('/' ,char ng)]<-string gn;b.[gn]<-ng) (List.except [n;i] z) g
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Seq.iter2 (fun ng gn->a.[(char n,char ng)]<-string gn;b.[gn]<-n+ng) z e
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Seq.iter2 (fun ng gn->a.[(char i,char ng)]<-string gn;b.[gn]<-i+ng) z l
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{n=char n;i=char i;g=a;e=b}
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