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pl:prolog:pllib:wolf_goat_cabbage [2019/06/27 15:50] (aktualna) |
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| + | ====== Wolf goat cabbage ====== | ||
| + | {{tag>puzzle}} | ||
| + | ===== Description ===== | ||
| + | Solving the wolf, goat, and cabbage problem | ||
| + | |||
| + | **Source**: The Art of Prolog | ||
| + | ===== Download ===== | ||
| + | Program source code: {{wolf_goat_cabbage.pl}} | ||
| + | ===== Listing ===== | ||
| + | <code prolog> | ||
| + | /* | ||
| + | States for the wolf, goat and cabbage problem are a structure | ||
| + | wgc(Boat,Left,Right), where Boat is the bank on which the boat | ||
| + | currently is, Left is the list of occupants on the left bank of | ||
| + | the river, and Right is the list of occupants on the right bank. | ||
| + | */ | ||
| + | initial_state(wgc,wgc(left,[wolf,goat,cabbage],[])). | ||
| + | |||
| + | final_state(wgc(right,[],[wolf,goat,cabbage])). | ||
| + | |||
| + | move(wgc(left,L,R),Cargo) :- member(Cargo,L). | ||
| + | move(wgc(right,L,R),Cargo) :- member(Cargo,R). | ||
| + | move(wgc(B,L,R),alone). | ||
| + | |||
| + | update(wgc(B,L,R),Cargo,wgc(B1,L1,R1)) :- | ||
| + | update_boat(B,B1), update_banks(Cargo,B,L,R,L1,R1). | ||
| + | |||
| + | update_boat(left,right). | ||
| + | update_boat(right,left). | ||
| + | | ||
| + | update_banks(alone,B,L,R,L,R). | ||
| + | update_banks(Cargo,left,L,R,L1,R1) :- | ||
| + | select(Cargo,L,L1), insert(Cargo,R,R1). | ||
| + | update_banks(Cargo,right,L,R,L1,R1) :- | ||
| + | select(Cargo,R,R1), insert(Cargo,L,L1). | ||
| + | |||
| + | insert(X,[Y|Ys],[X,Y|Ys]) :- | ||
| + | precedes(X,Y). | ||
| + | insert(X,[Y|Ys],[Y|Zs]) :- | ||
| + | precedes(Y,X), insert(X,Ys,Zs). | ||
| + | insert(X,[],[X]). | ||
| + | |||
| + | precedes(wolf,X). | ||
| + | precedes(X,cabbage). | ||
| + | |||
| + | legal(wgc(left,L,R)) :- not(illegal(R)). | ||
| + | legal(wgc(right,L,R)) :- not(illegal(L)). | ||
| + | |||
| + | illegal(Bank) :- member(wolf,Bank), member(goat,Bank). | ||
| + | illegal(Bank) :- member(goat,Bank), member(cabbage,Bank). | ||
| + | |||
| + | select(X,[X|Xs],Xs). | ||
| + | select(X,[Y|Ys],[Y|Zs]) :- | ||
| + | select(X,Ys,Zs). | ||
| + | |||
| + | % Program 20.2: Solving the wolf, goat, and cabbage problem | ||
| + | </code> | ||
| + | ===== Comments ===== | ||
